Digital load control system providing power and communication via existing power wiring

ABSTRACT

A two-way load control system comprises a power device, such as a load control device for controlling an electrical load receiving power from an AC power source, and a controller adapted to be coupled in series between the source and the power device. The load control system may be installed without requiring any additional wires to be run, and is easily configured without the need for a computer or an advanced commissioning procedure. The power device receives both power and communication over two wires. The controller generates a phase-control voltage and transmits a forward digital message to the power device by encoding digital information in timing edges of the phase-control voltage. The power device transmits a reverse digital message to the controller via the power wiring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a load control system for controllingthe amount of power delivered to an electrical load, such as a lightingload. More particularly, the present invention relates to a “two-wire”load control system having load control devices that receive both powerand communication over two wires from a digital controller that iseasily configured without the need for a computer or an advancedcommissioning procedure. In addition, the present invention relates to atwo-wire load control system having a plurality of load control devicesand a digital controller that may be installed in a pre-existingelectrical network without requiring any additional wiring. Further, thepresent invention relates to a two-wire load control system havingcontrollers that respond to a plurality of input devices and transmitdigital messages and power over two wires to load control deviceswithout interfering with other control devices on the electricalnetwork.

2. Description of the Related Art

In order for a gas discharge lamp, such as a fluorescent lamp, toilluminate, the lamp is typically driven by a ballast. The ballast maybe mounted in a lighting fixture in which the fluorescent lamp islocated, or to a junction box adjacent the lighting fixture. Electronicballasts receive alternating-current (AC) mains line voltage from an ACpower source and convert the AC mains line voltage to an appropriatevoltage waveform to drive the lamp. Many ballasts are simply switching(or non-dim) ballasts that are only able to turn the connectedfluorescent lamp on and off. To control a switching ballast, a standardwallbox-mounted mechanical switch is simply coupled in series electricalconnection between the AC power source and the ballast, such that a userturns the fluorescent lamp on and off by toggling the mechanical switch.Multiple switching ballasts may be coupled to a single mechanicalswitch, such that multiple fluorescent lamps can be turned on and offtogether in response to actuations of the single mechanical switch.

In contrast, dimming ballasts allow for control of the intensity of thecontrolled fluorescent lamp from a minimum intensity (e.g.,approximately 5%) to a maximum intensity (e.g., approximately 100%). Atypical prior art dimming ballast is operable to control the intensityof the controlled fluorescent lamp in response to a phase-controlvoltage (i.e., a dimmed-hot voltage) received from a dimmer switch. Thedimmer switch is electrically coupled between the AC power source andthe ballast (i.e., in the place of the mechanical switch that controls anon-dim ballast) and generally requires a connection to the neutral sideof the AC power source. There are typically three electrical connectionsto the prior art electronic dimming ballast: a switched-hot connection,a dimmed-hot connection, and a neutral connection. The switched-hotconnection receives a switched-hot voltage, which may be generated by arelay of the dimmer switch for turning the controlled lamp and theballast on and off. The ballast receives the phase-control voltage atthe dimmed-hot connection and is operable to determine a desiredlighting intensity in response to the length of a conduction period ofthe phase-control voltage.

It is often desirable to upgrade a non-dim ballast installation to havea dimming ballast to thus allow the user to adjust the intensity of thefluorescent lamp. In a standard non-dim installation, there is typicallyonly one electrical wire (i.e., a switched-hot voltage) coupled betweenthe electrical wallbox of the mechanical switch and the lighting fixturein which the ballast is located. Moreover, a neutral wire connectioncoupled to the neutral side of the AC power source may not be availablein the wallbox where the mechanical switch is located. However, it isdesirable to replace the non-dim ballast with the dimming ballast and toreplace the mechanical switch with the dimmer switch without running anyadditional electrical wiring between the dimmer switch and the dimmingballast (i.e., using only the pre-existing wiring). Running additionalwiring can be very expensive, due to the cost of the additionalelectrical wiring as well as the cost of installation. Typically,installing new electrical wiring requires a licensed electrician toperform the work (where simply replacing one ballast with anotherballast without running new wiring may not require a licensedelectrician). In addition, if the pre-existing wiring from themechanical switch to the ballast runs behind a fixed ceiling or wall(e.g., one comprising plaster or expensive hardwood), the electricianmay need to breach the ceiling or wall to install the new electricalwiring, which will thus require subsequent repair.

A further complication may arise when the existing ceiling containsasbestos. So long as the asbestos is not disturbed, it presents aminimal health hazard and may be left in place. However, if new wiringmust be installed between the dimmer switch and the dimming ballast,then the asbestos must be remediated. Such remediation must be performedby specially trained personnel. Also, the removed asbestos and assortedbuilding materials must be handled as hazardous waste. The process isexpensive and time consuming. Therefore, the prior art three-wiredimming ballast does not work well in retrofit installations asdescribed above because the ballast requires two electricalconnections—not one—between the dimmer switch and the ballast (i.e., theswitched-hot voltage and the dimmed-hot voltage) and the dimmer switchrequires connection to a neutral wire coupled to the neutral side of theAC power source in addition to the hot wire.

Some prior art dimming ballasts require only two connections (adimmed-hot connection for receiving the phase-control voltage and aneutral connection) and thus only a single electrical connection need bemade between the dimmer switch and the two-wire dimming ballast. Suchprior art two-wire dimming ballasts receive power (for driving thecontrolled lamp) and the phase-control voltage (for determining thedesired lighting intensity) over the single electrical connectionbetween the dimmer switch and the two-wire dimming ballasts. The desiredlighting intensity is proportional to the conduction period of thephase-control voltage. Accordingly, these two-wire ballasts may beinstalled in retrofit installations to replace non-dim ballast withoutsrunning any additional electrical wiring. A single dimmer switch maycontrol the intensities of multiple two-wire dimming ballasts coupled toreceive the phase-control voltage from the dimmer switch. However, thedimmer switch is only able to control the two-wire dimming ballasts inunison since each ballast receives the identical phase-control voltagefrom the dimmer switch. The dimmer switch cannot individually controlthe intensities of each of the ballasts coupled to the dimmer switch.Prior art two-wire ballasts are described in greater detail incommonly-assigned U.S. Pat. No. 6,111,368, issued Aug. 29, 2000,entitled SYSTEM FOR PREVENTING OSCILLATIONS IN A FLUORESCENT LAMPBALLAST, and U.S. Pat. No. 6,452,344, issued Sep. 17, 2002, entitledELECTRONIC DIMMING BALLAST, the entire disclosures of which are herebyincorporated by reference.

Some load control systems have digital electronic dimming ballasts thatallow control of individual lighting fixtures or groups of lightingfixtures independently of the electrical circuits to which the ballastsare wired for receiving power. Such load control systems typically havea controller coupled to the ballasts via a wired (low-voltage) digitalcommunication link (distinct from the power wiring) to allow for thecommunication of digital messages between the controller and theballasts. For example, the controller and ballasts may communicate usingthe industry-standard Digital Addressable Lighting Interface (DALI)communication protocol. The DALI protocol allows each DALI ballast inthe load control system to be assigned a unique digital address, to beprogrammed with configuration information (such as, for example, presetlighting intensities), and to control a fluorescent lamp in response tocommands transmitted via the communication link. Typically, a trainedinstaller is required to perform an advanced commissioning procedureusing a personal computer (PC) or other advanced programming tool toprogram the unique digital address and configuration information of theDALI ballasts.

Some DALI controllers may provide a user interface that allows forcontrol of the ballasts of the load control system. In addition, theload control system may include, for example, wall-mounted keypads orhandheld devices, such as infrared (IR) remote controls or personaldigital assistants (PDA), for controlling the electronic dimmingballasts. The IR commands are received by an IR receiving sensor thatsends appropriate commands to the controlled ballasts. In addition to IRreceiving sensors, the load control system may also include daylightsensors or occupancy sensors. The daylight and occupancy sensors monitorthe condition (e.g., the ambient light level or motion from an occupant,respectively) of a space and send appropriate commands to the controlledballasts in response to the sensed conditions in the space. Examples ofdigital electronic dimming ballasts are described in greater detail incommonly-assigned U.S. Pat. No. 7,619,539, issued Nov. 17, 2009,entitled MULTIPLE-INPUT ELECTRONIC DIMMING BALLAST WITH PROCESSOR, andU.S. Pat. No. 8,035,529, issued Oct. 11, 2011, entitled DISTRIBUTEDINTELLIGENCE BALLAST SYSTEM, the entire disclosures of which are herebyincorporated by reference.

The prior art digital dimming ballasts require that the wired digitalcommunication link is coupled to each of the ballasts—in addition to thepower wiring—and thus are not well suited to retrofit installations,where the digital dimming ballasts are replacing non-dimming ballasts.To address these limitations, some prior art control systems haveprovided for digital communication between control devices over theexisting power wiring coupled to the devices. For example, in apower-line carrier (PLC) communication system, such as an X10 controlsystem, the control devices are able to modulate high-frequency digitalmessages on the AC mains line voltage provided on the power wiring(e.g., referenced between hot and neutral of the AC power source).Examples of power-line carrier communication systems are described ingreater detail in U.S. Pat. No. 4,200,862, issued Apr. 29, 1980,entitled APPLIANCE CONTROL, and U.S. Pat. No. 4,418,333, issued Nov. 29,1983, entitled APPLIANCE CONTROL SYSTEM, the entire disclosures of whichare hereby incorporated by reference.

However, such power-line carrier communication systems have manydisadvantages that have prevented the systems from enjoying widecommercial success. Typically, the control devices of power-line carriercommunication systems require connections to both the hot side and theneutral side of the AC power source, which connections may not both beavailable in the electrical wallboxes of a retrofit installation. Inaddition, since the control devices reference the transmitted signalsbetween hot and neutral, the signals are able to travel throughout thepower system, and thus may cause noise and interference with othercontrol devices coupled to the power system. Often, such systems requireback filters to prevent the communication signals from being transmittedthroughout the power system. In addition, large reactive elements (i.e.,capacitances) coupled across the AC power source can attenuate thedigital messages transmitted by the control devices thus degrading thequality of the transmitted digital messages and decreasing thereliability of the communications of the system.

Attempts have been made to design power-line control systems that avoidthe disadvantages of the above-referenced prior art power-line carriercommunication systems. U.S. Pat. No. 5,264,823, issued Nov. 23, 1993,entitled POWER LINE COMMUNICATION SYSTEM (referred to herein as the '823patent), discloses a system in which data is transmitted on a power lineby means of momentary interruptions of the power at or near thezero-crossings of an AC waveform. The '823 patent teaches that differentpatterns of interruptions can represent different digital “words.” Theinterruptions form “notches” in an otherwise sinusoidal AC waveform. Areceiver is configured to detect the presence of the “notches,” tocompare detected patterns of “notches” with pre-stored values, and torespond if a match is found with a detected pattern.

The '823 patent proposes techniques for detecting power interruptions ator near zero-crossings, a number of which techniques are complex andsubject to error. For example, a power interruption that occurs near azero-crossing, as the '823 patent proposes, may not be reliably detecteddue to the existence of “noise” on the AC mains line. A powerinterruption that occurs away from a zero-crossing, according to the'823 patent, assertedly can be detected by “pattern recognition of somesort” or by performing “a fast Fourier transform of the waveform” andlooking for “selected high order coefficients to detect a notch.” Suchprocesses would be costly and complex to implement, and would also besusceptible to errors due to the existence of “noise” on the AC mainsline. The system disclosed in the '823 patent also has very low datatransfer rates, with at most one bit being transferred per complete ACcycle. A multi-bit message would occupy at least as many complete ACcycles in the '823 patent, and potentially twice as many cycles ifconsecutive positive half-cycles or zero-crossings were used.

U.S. Pat. No. 6,784,790, issued Aug. 31, 2004, entitledSYNCHRONIZATION/REFERENCE PULSE-BASED POWERLINE PULSE POSITION MODULATEDCOMMUNICATION SYSTEM (referred to herein as the '790 patent), disclosesa system in which control devices generate high frequency voltage pulseson the AC mains line voltage and transmit data by means of timedintervals between the pulses. In an attempt to avoid communicationerrors as a result of the attenuation of transmitted signals (which is aproblem of the prior art power-line carrier communication systems), the'790 patent proposes use of the high-frequency voltage pulses that occurnear zero-crossings and whose magnitude is much larger, relative to theAC power line voltage, than the carrier voltage pulses utilized inearlier prior art power-line carrier communication systems.

The system disclosed in the '790 patent involves superimposing a carriersignal on AC mains voltage. The transmitter in the '790 patent requiresa connection to both the hot side and the neutral side of the AC powersource and thus would not work in many retrofit situations. Thehigh-frequency voltage pulses are generated near the zero-crossings ofthe AC power source and may produce noise that could cause communicationerrors at other control devices. In addition, since the high-frequencypulses generated by the control devices of the '790 patent look verysimilar to typical noise generated by other electrical devices on the ACmains line voltage, the control devices may be susceptible tocommunication reception errors. Further, and despite their magnituderelative to AC mains voltage, the pulses proposed in the '790 patentwould be susceptible to attenuation due to large reactive elementscoupled across the AC power source.

U.S. Pat. No. 8,068,014, issued Nov. 29, 2011, entitled SYSTEM FORCONTROL OF LIGHTS AND MOTORS, discloses a system in which data istransmitted by means of a carrier signal superimposed on the loadcurrent of an isolated load control system rather than AC mains linevoltage. The system includes a transmitting device coupled in seriesbetween an AC power source and a load control device, which is coupledto an electrical load for regulating the load current conducted throughthe load. If there are multiple load control devices in acurrent-carrier communication system, the load current that is conductedby the transmitting device is divided between the multiple load controldevices. Accordingly, the magnitude of each high-frequency digitalmessage modulated onto the load current is attenuated (i.e., by currentdivision) and the quality of the digital messages may be degraded.

Despite decades of attempts to develop practical power line carrierlighting control systems, there continues to be a need for apparatusthat can reliably communicate data over a single power line between adimmer switch and an electronic dimming ballast in a low-cost lightingcontrol system. There also continues to be a need for low cost apparatusthat can reliably and selectively control a plurality of fluorescent orlight-emitting diode (LED) lighting fixtures connected to a singlecontroller by a single power line. In addition, there continues to be aneed for low cost PLC apparatus that is suitable for upgrading a simple,non-dim lighting system to a dimmed lighting system without the need foradditional wiring or a complex commissioning process.

SUMMARY OF THE INVENTION

As described herein, a two-way load control system for controlling anelectrical load receiving power from an alternating-current (AC) powersource comprises a power device (e.g., a load control device forcontrolling the electrical load or an input device) and a controllerthat is adapted to be coupled in series electrical connection betweenthe AC power source and the power device. The load control system may beinstalled without requiring any additional wires to be run. The powerdevice receives both power and communication from the controller overtwo wires (e.g., the pre-existing wiring). The controller may be coupledto the neutral side of the AC power source (if available), but does notrequire a connection to neutral.

Rather than modulating high-frequency digital messages or pulses ontothe AC mains line voltage to communicate with the power devices, thecontroller generates a phase-control voltage having a variable timingedge (i.e., phase angle). Specifically, the controller transmits“forward” digital messages to the power devices by modulating the timingedges of the phase-control voltage relative to a reference edge, i.e.,digital information is encoded in the timing between the edges. Thetiming of the edges of the phase-control voltage can be controlledprecisely by the controller and detected reliably by each power device,which does not require a zero-crossing detector to detect the timingedges of the phase-control voltage. Each power device is operable totransmit a “reverse” digital message to the controller and the otherpower devices of the load control system in response to receiving aforward digital message. Specifically, the power device is operable tomodify the phase-control voltage generated by the controller to transmitreverse digital messages.

Since the controller generates a phase-control voltage for communicatingdigital information to the power device, the electrical hardware of thecontroller is very similar to that of a standard dimmer switch. Inaddition, the controller is able to “swallow” the phase-control signal,such that the phase-control signal only exists on the power wiringbetween the controller and the power device, and does not generate noisethat interferes with other control devices coupled to the power wiring.In other words, the phase-control signal only travels downstream fromthe controller to the power device, and not upstream from the controllerto the AC power source. Since the controller and the power devices donot modulate high-frequency digital messages onto the AC mains linevoltage, large reactive elements coupled across the AC power source donot degrade the quality of the digital messages transmitted by thecontroller to the power device.

The load control system may comprise a plurality of power devices. Forexample, the load control system may comprise a plurality of loadcontrol devices that are operable to control respective electrical loadsand are coupled to the controller via a single circuit wiring. Differenttypes of load control devices may be mixed on a single circuit andcontrolled by the controller. The load control devices may comprise, forexample, a dimming ballast for driving a gas-discharge lamp; alight-emitting diode (LED) driver for driving an LED light source; adimming circuit for controlling the intensity of a lighting load; ascrew-in luminaire including a dimmer circuit and an incandescent orhalogen lamp; a screw-in luminaire including a ballast and a compactfluorescent lamp; a screw-in luminaire including an LED driver and anLED light source; an electronic switch, controllable circuit breaker, orother switching device for turning an appliance on and off; a plug-inload control device, controllable electrical receptacle, or controllablepower strip for controlling one or more plug-in loads; a motor controlunit for controlling a motor load, such as a ceiling fan or an exhaustfan; a drive unit for controlling a motorized window treatment or aprojection screen; motorized interior or exterior shutters; a thermostatfor a heating and/or cooling system; a temperature control device forcontrolling a setpoint temperature of an HVAC system; an airconditioner; a compressor; an electric baseboard heater controller; acontrollable damper; a variable air volume controller; a fresh airintake controller; a ventilation controller; a hydraulic valves for useradiators and radiant heating system; a humidity control unit; ahumidifier; a dehumidifier; a water heater; a boiler controller; a poolpump; a refrigerator; a freezer; a television or computer monitor; avideo camera; an audio system or amplifier; an elevator; a power supply;a generator; an electric charger, such as an electric vehicle charger;and an alternative energy controller.

The load control system may be configured and re-configured withoutrequiring a computer or an advanced commissioning procedure and withoutrequiring access to the power devices (which may be remotely located andnot easily accessible). Since the power devices are operable to transmitreverse digital message to the controller, the controller is able toassigned unique addresses to each of the power devices by transmittingforward digital messages to the power devices, for example, using a“soft addressing” procedure. The power devices may also be assigned togroups (i.e., zone), such that the controller is able transmit digitalmessages to the power devices to control the loads individually or inthe groups. In particular, when the power devices comprise ballasts, theballasts may be installed just like a prior art non-dim ballast sincethe ballasts are each assigned a link address during the soft addressingprocedure. Prior to being assigned link addresses by the controller, thepower devices are operable to work out-of-box as a single group. Inaddition, the load control system provides for easy replacement ofmissing or faulty power devices. When a missing or faulty power deviceis replaced by a new power device, the controller is able toautomatically detect the new power device and to program the new powerdevice with the operational settings of the old power device. Since theload control system may be installed without requiring any additionalwiring and is easily programmed, the load control system may beconfigured prior to shipment as a pre-programmed system that can simplybe installed and is then fully operational immediately upon first powerup.

Further, the load control system may comprise a plurality ofcontrollers, each coupled to one or more load control devices via aseparate circuit wiring. In addition, the controllers may be operable totransmit digital messages to the load control devices to control theloads in response to input signals received from input devices to allowfor both local and central control of the loads. For example, thecontrollers may be operable to receive radio-frequency (RF) signals froma plurality of RF transmitters. Accordingly, the controllers may beoperable to control the electrical loads in response to the RFtransmitters in groups that are independent of the separate circuitwirings. The input devices (i.e., the RF transmitters and the powerdevices) of the load control system may comprise, for example, occupancysensors, vacancy sensors, daylight sensors, radiometers, cloudy-daysensors, temperature sensors, humidity sensors, pressure sensors, smokedetectors, carbon monoxide detectors, air-quality sensors, securitysensors, proximity sensors, fixture sensors, partition sensors, keypads,battery-powered remote controls, kinetic or solar-powered remotecontrols, key fobs, cell phones, smart phones, tablets, personal digitalassistants, personal computers, laptops, timeclocks, audio-visualcontrols, safety devices, power monitoring devices (such as powermeters, energy meters, utility submeters, utility rate meters), centralcontrol transmitters, residential, commercial, or industrialcontrollers, or any combination of these input devices.

Because the power devices are able to transmit the reverse digitalmessages in response to receiving forward digital messages, thecontroller can receive feedback information from the power devices. Forexample, when the power devices comprise ballasts, the ballasts maytransmit present light intensities of the controlled lamps orinformation regarding lamp status information (such as indications ofmissing or failed lamps) to the controller. Alternatively, an occupancysensor could transmit information regarding occupancy and vacancyconditions and a daylight sensor could transmit a measured light levelto the controller. The controller could be operable to transmit thereceived feedback information to an external device, such as a centralcontroller that is coupled to a network.

Each power devices is able to transmit an acknowledgement to thecontroller in response to receiving a forward digital message, such thatthe controller is able to confirm that all of the power devices receivedthe forward digital message. Accordingly, the controller is operable totransmit new values of operating settings and updated firmware to thepower devices via forward digital messages. This allows the load controlsystem to adapt to new types of power devices and changes in thefunctionality of power devices after installation.

Accordingly, the load control system is able to provide all of theadvantages of a load control system having a two-way digitalcommunication link without requiring any additional wiring. This meansthat the load control system appears the same as the prior art digitalload control systems during programming and normal operation, but isvastly easier to install.

As described herein, a load control system comprises a power deviceadapted to receive power from an AC power source via a power wiring anda controller adapted to be coupled in series electrical connection onthe power wiring between the AC power source and the power device, suchthat two-way communication is provided between the controller and thepower device via phase-control signals generated on the power wiring.The controller is operable to transmit a forward digital message to thepower device by encoding digital information in timing edges of aphase-control voltage generated on the power wiring by the controller,and the power device is operable to transmit a reverse digital messageto the controller via the power wiring.

According to an embodiment, a load control system comprises a powerdevice adapted to receive power from an AC power source via a powerwiring and a controller adapted to be coupled in series electricalconnection on the power wiring between the AC power source and the powerdevice, such that two-way communication is provided between thecontroller and the power device via phase-control signals generated onthe power wiring. The controller is operable to transmit a forwarddigital message to the power device by encoding digital information intiming edges of a phase-control voltage generated on the power wiring bythe controller, and the power device is operable to transmit a reversedigital message to the controller via the power wiring. The power devicemay comprise an input device or a load control device for controlling anelectrical load.

According to another embodiment, a controller for use in a load controlsystem for controlling the power delivered from an AC power source to anelectrical load comprises a controllably conductive device, a controlcircuit, and a reverse receiving circuit. The controllably conductivedevice is adapted to be coupled in series electrical connection on apower wiring between the AC power source and a power device of the loadcontrol system. The control circuit is coupled to the controllablyconductive device for rendering the controllably conductive deviceconductive each half-cycle of the AC power source to generate aphase-control voltage. The control circuit is operable to transmit aforward digital message to the power device by encoding digitalinformation in timing edges of the phase-control voltage. The reversereceiving circuit is coupled in parallel electrical connection with thecontrollably conductive device. The control circuit is operativelycoupled to the reverse receiving circuit for receiving a reverse digitalmessage from the power device via the power wiring.

According to yet another embodiment, a power device for use in a loadcontrol device for controlling the power delivered from an AC powersource to an electrical load in response to a controller comprises acontrol circuit, a forward receiving circuit, and a reverse transmittingcircuit. The forward receiving circuit is adapted to be coupled to thecontroller via a power wiring, such that the controller is coupled inseries electrical connection between the AC power source and the powerdevice. The forward receiving circuit is operable to receive aphase-control voltage from the controller via a power wiring. Thecontrol circuit is operatively coupled to the forward receiving circuitfor receiving a forward digital message in response to digitalinformation encoded in timing edges of the phase-control voltage. Thereverse transmitting circuit is adapted to be coupled to the controllervia the power wiring. The control circuit is operatively coupled to thereverse transmitting circuit for transmitting a reverse digital messageto the controller via the power wiring.

In addition, a retrofit kit comprises a load control device adapted toreceive power from an AC power source via a power wiring and to controlthe power delivered from the AC power source to an electrical load. Theload control device is operable to receive a phase-control voltage viathe power wiring, to control the power delivered to the load in responseto digital information encoded in timing edges of the phase-controlvoltage, and to transmit a reverse digital message via the power wiring.

In addition, a method of communicating digital messages between acontroller to a power device coupled to a power wiring is also describedherein. The method comprises: (1) the controller generating aphase-control voltage across the power device; (2) the controllertransmitting a forward digital message by encoding digital informationin the timing edges of the phase-control voltage; (3) the power devicedecoding the forward digital message from the digital informationencoded in the timing edges of the phase-control voltage; and (4) thepower device transmitting a reverse digital message to the controllervia the power wiring.

According to another embodiment, a load control system comprises aplurality of power devices adapted to be coupled in parallel with eachother and operable to receive power from an AC power source via a powerwiring, and a controller adapted to be coupled in series electricalconnection on the power wiring between the AC power source and theparallel combination of the power devices. The controller is operable toproduce a phase-control voltage that is adapted to be received by thepower devices, and to transmit a first digital message to the powerdevices via the power wiring by encoding digital information in timingedges of the phase-control voltage. At least one of the power device isoperable to transmit a reverse digital message via the power wiring.

According to another embodiment, a load control system comprises a powerdevice adapted to receive power from an AC power source via a powerwiring, and a controller adapted to be coupled in series electricalconnection on the power wiring between the AC power source and the powerdevice. The controller is operable to produce a phase-control voltage onthe power wiring between the controller and the power device. The powerdevice is operable to receive the phase-control voltage and to transmitfeedback to the controller via the power wiring in response to thephase-control voltage.

According to another embodiment, a load control system comprises a powerdevice adapted to receive power from an AC power source via a powerwiring, and a controller adapted to be coupled in series electricalconnection on the power wiring between the AC power source and the powerdevice. The controller is configured to produce a phase-control voltagethat is adapted to be received by the power device, and is configured totransmit a forward digital message to the power device by encodingdigital information in timing edges of the phase-control voltage. Thepower device is configured to transmit a reverse digital message to thecontroller via the power wiring. The controller is configured totransmit a short pattern immediately prior to the power devicetransmitting the reverse digital message, where the short pattern has alength less than the length of the forward digital message.

According to another embodiment, a load control system comprises aplurality of power devices adapted to be coupled in parallel with eachother and operable to receive power from an AC power source via a powerwiring, and a controller adapted to be coupled in series electricalconnection on the power wiring between the AC power source and theparallel combination of the power devices. The controller is operable toproduce a phase-control voltage that is adapted to be received by thepower devices, and is configured to transmit a first digital message tothe power devices via the power wiring by encoding digital informationin timing edges of the phase-control voltage. At least one of the powerdevice is operable to transmit a reverse digital message via the powerwiring. The controller is configured to transmit a short patternimmediately prior to the power device transmitting the reverse digitalmessage, where the short pattern has a length less than the length ofthe forward digital message.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple wiring diagram of a lighting control system having aplurality of two-wire digital dimming ballasts and a digital ballastcontroller.

FIG. 2A shows example input devices of the load control system of FIG.1.

FIG. 2B shows example form factors of the digital ballast controller ofthe load control system of FIG. 1.

FIG. 2C shows example electrical load and load control devices of theload control system of FIG. 1.

FIG. 3A is a simplified block diagram of a digital ballast controller.

FIG. 3B is a simplified block diagram of a digital dimming ballast.

FIGS. 4A and 4B are floor plan diagrams of example installations oflighting control system in a classroom.

FIG. 5 is a simplified perspective view of a retrofit kit having adigital dimming ballasts pre-wired to lamp sockets and mounted to a pan.

FIGS. 6A and 6B are example timing diagrams of a control-hot voltagegenerated by a digital ballast controller for communicating digitalmessages to a digital dimming ballast.

FIG. 7 is an example diagram of a message structure for a digitalmessage transmitted by a digital ballast controller to a digital dimmingballast.

FIG. 8 is an example timing diagram of a control-hot voltage showing astart pattern including a unique start symbol generated by a digitalballast controller for starting a digital message transmitted to adigital dimming ballasts.

FIG. 9 is a simplified flowchart of a button procedure executed by adigital ballast controller in response to an actuation of an actuator ofthe digital ballast controller.

FIGS. 10A and 10B are simplified flowcharts of a radio-frequency (RF)message procedure executed by a digital ballast controller when adigital message is received from an RF transmitter.

FIG. 11 is a simplified flowchart of a zero-crossing procedure executedby a ballast controller.

FIG. 12 is a simplified flowchart of a timer interrupt procedureexecuted by a digital ballast controller.

FIG. 13 is a simplified flowchart of a data edge procedure executed by adigital ballast controller.

FIG. 14 is a simplified flowchart of a receiving procedure executed by adigital dimming ballast to receive a digital message transmitted by adigital ballast controller.

FIG. 15 is a simplified flowchart of a receive data procedure executedby a digital dimming ballast to determine the bits of data of a receiveddigital message.

FIG. 16 is an example timing diagram of a control-hot voltage having twodata edges per one reference edge.

FIG. 17 is an example timing diagram of a control-hot voltage showing astart pattern.

FIG. 18 is a simplified flowchart of a timer interrupt procedureexecuted by a digital ballast controller to generate reference and dataedges of a transmitted digital message.

FIG. 19 is a simplified flowchart of a receiving procedure executed by adigital dimming ballast to receive a digital message from a digitalballast controller.

FIG. 20 is a simplified block diagram of a lighting control systemcomprising a two-wire digital ballast controller that does not require aneutral connection and an active load circuit.

FIG. 21 is a simplified block diagram of a digital ballast controllerand an active load circuit.

FIG. 22 is a simplified block diagram of a lighting control systemcomprising a digital dimming ballast that is directly connected to oneor more input devices.

FIG. 23 is a simple wiring diagram of a lighting control system having aplurality of two-wire LED drivers and a digital LED controller.

FIG. 24 is a simple wiring diagram of a two-way load control systemhaving a plurality of two-wire power devices (e.g., digital dimmingballasts and input devices) and a digital power device controller.

FIG. 25 is a simplified block diagram of a digital power devicecontroller.

FIG. 26 is a simplified block diagram of a digital dimming ballast.

FIG. 27 is a simplified schematic diagram of a power converter for anelectronic ballast.

FIG. 28A is an example diagram of a “forward” digital messagetransmitted from a digital power device controller to a power device anda “reverse” digital message transmitted from the power device to thedigital power device controller.

FIG. 28B is an example timing diagram of a control-hot voltage showing astart pattern.

FIGS. 29A and 29B are example timing diagrams of a control-hot voltageand a controller-drop voltage showing example reverse data patterns ofthe reverse digital messages.

FIG. 30 is a simplified flowchart of a timer interrupt procedureexecuted by a digital power device controller.

FIG. 31 is a simplified flowchart of a forward transmitting procedureexecuted by a digital power device controller.

FIG. 32 is a simplified flowchart of a reverse receiving procedureexecuted by a digital power device controller.

FIG. 33 is a simplified flowchart of a receive data procedure executedby a digital power device controller.

FIG. 34 is a simplified flowchart of a zero-crossing procedure executedby a digital dimming ballast.

FIG. 35 is a simplified flowchart of a rising edge procedure executed bya digital dimming ballast.

FIG. 36 is a simplified flowchart of a forward receiving procedureexecuted by a digital dimming ballast.

FIG. 37 is a simplified flowchart of a reverse transmitting procedureexecuted by a digital dimming ballast.

FIG. 38 is a simplified flowchart of a reverse transmit data procedureexecuted by a digital dimming ballast.

FIG. 39A is an example diagram of a message structure for a digitalmessage transmitted by a digital power device controller to a powerdevice.

FIGS. 39B-39H are simple diagrams of forward digital messagestransmitted from a digital ballast controller to a power device andreverse digital messages transmitted from the power device to thedigital ballast controller.

FIG. 40 is a simple timing diagram of a control-hot voltage and acontroller-drop voltage showing an example reverse digital message.

FIG. 41 is a simplified block diagram of an example digital dimmingballast that is able to communicate via a circuit wiring of the loadcontrol system, as well as communicate via a wired digital communicationlink.

FIG. 42 is a simplified block diagram of an example digital dimmingballast that is able to communicate and receive power via a circuitwiring.

FIG. 43 is a simplified block diagram of another example digital dimmingballast that is able to communicate and receive power via a circuitwiring.

FIG. 44 is a simplified schematic diagram of an example power supply foran electronic ballast.

FIG. 45 is a simplified schematic diagram of another example powersupply for an electronic ballast.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 1 is a simple wiring diagram of a load control system 100 having aplurality of two-wire power devices (e.g., two-wire load controldevices, such as two-wire digital dimming ballasts 110). The two-wiredigital dimming ballasts 110 are coupled to respective lamps 104 forcontrolling the intensities of the lamps to a desired lighting intensityL_(DES) between a low-end (i.e., minimum) intensity L_(LE) (e.g.,approximately 1%) and a high-end (i.e., maximum) intensity L_(HE) (e.g.,approximately 100%). The load control system 100 also comprises adigital ballast controller 120 (i.e., a remote control device) that isadapted to be coupled in series electrical connection between analternating-current (AC) power source 102 and the two-wire digitaldimming ballasts 110 via a circuit wiring 114. In other words, eachdigital dimming ballast 110 is coupled in series with the digitalballast controller 120 across the AC power source 102. As shown in FIG.1, the digital ballast controller 120 may be directly coupled to theneutral side of the AC power source 102. The circuit wiring 114 may bethe pre-existing wiring of the electrical network of the building inwhich the load control system 100 is installed and may be located in theinterior and exterior of the building.

The two-wire digital dimming ballasts 110 are coupled in parallel andreceive both power and digital communication from a control-hot voltageV_(CH) (i.e., a phase-control voltage) that is generated by the digitalballast controller 120 as will be described in greater detail below. Thecontrol-hot voltage V_(CH) generated by the digital ballast controller120 differs from the phase-control voltage received by prior artthree-wire and two-wire dimming ballasts in that the digital dimmingballasts 110 of the load control system 100 do not determine the desiredlighting intensity L_(DES) for the respective lamp 104 in response tothe length of the conduction period of the control-hot voltage V_(CH).Rather, the two-wire digital dimming ballasts 110 of the load controlsystem 100 are able to determine the desired lighting intensity L_(DES)(i.e., are controlled to a defined state) in response to the digitalcontrol information (i.e., digital communication messages) derived fromthe control-hot voltage V_(CH).

As shown in FIG. 1, the digital ballast controller 120 may be a wallboxdevice, i.e., adapted to be wall-mounted in a standard single-gangelectrical wallbox, thus replacing a standard mechanical switch that mayhave been controlling the power delivered to the previous ballasts andlamps prior to installation of the digital ballast controller. Thedigital ballast controller 120 comprises a faceplate 122 and a userinterface that is received in an opening of the faceplate and includes atoggle actuator 124 and an intensity adjustment actuator 126 forreceiving user inputs to control the fluorescent lamps 104. The digitalballast controller 120 communicates with the digital dimming ballasts110 to cause the fluorescent lamps 104 to toggle, i.e., turn off and on,in response to actuations of the toggle actuator 124. The digitalballast controller 120 increases and decreases the lighting intensity ofthe fluorescent lamps 104 in response to actuations of an upper portion126A or a lower portion 126B of the intensity adjustment actuator 126,respectively. The user interface of the digital ballast controller 120also includes a plurality of visual indicators 128, e.g., light-emittingdiodes (LEDs), which are arranged in a linear array and are illuminatedto provide feedback of the intensity of the fluorescent lamps 104.

The load control system 100 may also comprise a plurality of inputdevices, for example, wireless transmitters, such as a wirelessoccupancy sensor 130, a wireless daylight sensor 140, and a wirelessbattery-powered remote control 150, which are operable to transmitdigital messages (i.e., input signals) to the digital ballast controller120 via radio-frequency (RF) signals 106. The digital ballast controller120 is operable to turn the fluorescent lamps 104 on and off and adjustthe intensities of the fluorescent lamps 104 in response to the digitalmessages received from the occupancy sensor 130, the daylight sensor140, and the battery-powered remote control 150. The wirelesstransmitters may be operable to transmit the digital messages to thedigital ballast controller 120 according to a predefined RFcommunication protocol, such as, for example, one of LUTRON CLEARCONNECT, WIFI, ZIGBEE, Z-WAVE, KNX-RF, and ENOCEAN RADIO protocols.Alternatively, the wireless transmitters could transmit the digitalmessages via a different wireless medium, such as, for example, infrared(IR) signals or sound (such as voice). The digital ballast controller120 may be operable to transmit digital messages to the digital dimmingballasts 110 via the control-hot voltage V_(CH) in response to receivingRF signals from via a wireless network (i.e., via the Internet).

Because the digital dimming ballasts 110 are typically mounted insidemetal lighting fixtures, the digital dimming ballasts 110 are typicallynot able to receive the RF signals 106 from the wireless transmitters.However, since the digital ballast controller 120 transmits digitalmessages to the digital dimming ballasts 110 via the control-hot voltageV_(CH) in response to receiving the RF signals 106 from the wirelesstransmitters, the fluorescent lamps 104 are able to be controlled inresponse to the wireless transmitters.

During a setup procedure of the load control system 100, the digitalballast controller 120 is associated with the occupancy sensor 130, thedaylight sensor 140, and the battery-powered remote control 150, forexample, by pressing an actuator on the wireless transmitter andpressing an actuator on the digital ballast controller (e.g., the toggleactuator 124). All digital messages transmitted to the digital ballastcontroller 120 by the occupancy sensor 130, the daylight sensor 140, andthe battery-powered remote control 150 may include a command andidentifying information, for example, a serial number (i.e., a uniqueidentifier) associated with the wireless transmitter. The digitalballast controller 120 is responsive to messages containing the serialnumbers of the occupancy sensor 130, the daylight sensor 140, and thebattery-powered remote control 150 to which the digital ballastcontroller is associated.

The occupancy sensor 130 may be removably mountable to a ceiling (asshown in FIG. 1) or to a wall, for example, in the vicinity of (i.e., aspace around) the fluorescent lamps 104 controlled by the ballasts 110.The occupancy sensor 130 is operable to detect occupancy conditions inthe vicinity of the fluorescent lamps, and includes an internaloccupancy detection circuit, e.g., having a pyroelectric infrared (PIR)detector, which is housed in an enclosure 132 having a lens 134. Theinternal detector is operable to receive infrared energy from anoccupant in the space via the lens 134 to thus sense the occupancycondition in the space. The occupancy sensor 130 is operable to processthe output of the PIR detector to determine whether an occupancycondition (i.e., the presence of the occupant) or a vacancy condition(i.e., the absence of the occupant) is presently occurring in the space,for example, by comparing the output of the PIR detector to apredetermined occupancy voltage threshold. Alternatively, the internaldetector could comprise an ultrasonic detector, a microwave detector, orany combination of PIR detectors, ultrasonic detectors, and microwavedetectors.

The occupancy sensor 130 operates in an “occupied” state or a “vacant”state in response to the detections of occupancy or vacancy conditions,respectively, in the space. If the occupancy sensor 130 is in the vacantstate and the occupancy sensor determines that the space is occupied inresponse to the PIR detector, the occupancy sensor changes to theoccupied state. The occupancy sensor 130 transmits digital messageswirelessly via RF signals 106 to the digital ballast controller 120 inresponse to the present state of the occupancy sensor. The commandsincluded in the digital messages transmitted to the digital ballastcontroller 120 by the occupancy sensor 130 may comprise an occupiedcommand or a vacant command.

When the fluorescent lamps 104 are off, the digital ballast controller120 is operable to turn on the fluorescent lamps in response toreceiving the occupied command from the occupancy sensor 130. Thedigital ballast controller 120 is operable to turn off the fluorescentlamps 104 in response to receiving the vacant command from the occupancysensor 130. If there were more than one occupancy sensor 130 in the loadcontrol system 100, the digital ballast controller 120 would turn on thefluorescent lamps 104 in response to receiving a first occupied commandfrom any one of the occupancy sensors, and turn off the fluorescentlamps in response to the last vacant command received from thoseoccupancy sensors from which the occupancy sensor received occupiedcommands. For example, if two occupancy sensors 130 both transmitoccupied commands to the digital ballast controller 120, the digitalballast controller will not turn off the fluorescent lamps 104 untilsubsequent vacant commands are received from both of the occupancysensors. Accordingly, the occupancy sensor 130 provides automaticcontrol and energy savings by turning off the fluorescent lamps 104 whenthe space is unoccupied.

Alternatively, the occupancy sensor 130 could be implemented as avacancy sensor. The digital ballast controller 120 would only operate toturn off the fluorescent lamps 104 in response to receiving the vacantcommands from the vacancy sensor. Therefore, if the load control system100 includes vacancy sensors, the fluorescent lamps 104 must be turnedon manually (e.g., in response to a manual actuation of the toggleactuator 124 of the digital ballast controller 120). Examples of RF loadcontrol systems having occupancy and vacancy sensors are described ingreater detail in commonly-assigned U.S. patent application Ser. No.12/203,518, filed Sep. 3, 2008, entitled RADIO-FREQUENCY LIGHTINGCONTROL SYSTEM WITH OCCUPANCY SENSING; U.S. patent application Ser. No.12/203,500, filed Sep. 3, 2008, entitled BATTERY-POWERED OCCUPANCYSENSOR; and U.S. patent application Ser. No. 12/371,027, filed Feb. 13,2009, entitled METHOD AND APPARATUS FOR CONFIGURING A WIRELESS SENSOR,the entire disclosures of which are hereby incorporated by reference.

The daylight sensor 140 is mounted so as to measure a total lightintensity in the space around the daylight sensor (i.e., in the vicinityof the fluorescent lamps 104). The daylight sensor 140 includes aninternal photosensitive circuit, e.g., a photosensitive diode, which ishoused in an enclosure 142 having a lens 144 for conducting light fromoutside the daylight sensor towards the internal photosensitive diode.The daylight sensor 140 is responsive to the total light intensitymeasured by the internal photosensitive circuit. Specifically, thedaylight sensor 140 is operable to wirelessly transmit digital messagesincluding a value representative of the total light intensity to thedigital ballast controller 120 via the RF signals 106. The digitalballast controller 120 automatically adjusts the lighting intensities ofthe fluorescent lamps 104 in response to the total light intensitymeasured by the daylight sensor 140, so as to reduce the total powerconsumed by the load control system 100. If there is more than onedaylight sensor 140 in the load control system 100, the digital ballastcontroller 120 may be operable to, for example, average the values ofthe total light intensities measured by multiple daylight sensors 140and then adjust the intensities of the fluorescent lamps 104 in responseto the average of the values of the total light intensities measured bymultiple daylight sensors. Examples of RF load control systems havingdaylight sensors are described in greater detail in commonly-assignedU.S. patent application Ser. No. 12/727,956, filed Mar. 19, 2010,entitled WIRELESS BATTERY-POWERED DAYLIGHT SENSOR, and U.S. patentapplication Ser. No. 12/727,923, filed Mar. 19, 2010, entitled METHOD OFCALIBRATING A DAYLIGHT SENSOR, the entire disclosures of which arehereby incorporated by reference.

The battery-powered remote control 150 comprises an on button 152, anoff button 154, a raise button 155, a lower button 156, and a presetbutton 158 for providing manual control of the fluorescent lamps 104 bya user of the load control system 100. The remote control 150 isoperable to transmit digital messages including commands to control thefluorescent lamps 104 to the digital ballast controller 120 in responseto actuations of the buttons 152-158. Specifically, the battery-poweredremote control 150 simply transmits information regarding which of thebuttons 152-158 was actuated to the digital ballast controller 120 viathe RF signals 106. The digital ballast controller 120 turns thefluorescent lamps 104 on and off in response to actuations of the onbutton 152 and the off button 154 of the remote control 150,respectively. The digital ballast controller 120 raises and lowers theintensity of the fluorescent lamps 104 in response to actuations of theraise button 155 and the lower button 156, respectively. The digitalballast controller 120 controls the intensity of each of the fluorescentlamps 104 to a preset intensity in response to actuations of the presetbutton 158. Examples of battery-powered remote controls are described ingreater detail in commonly-assigned U.S. patent application Ser. No.12/399,126, filed Mar. 6, 2009, entitled WIRELESS BATTERY-POWERED REMOTECONTROL HAVING MULTIPLE MOUNTING MEANS, and U.S. Pat. No. 7,573,208,issued Aug. 22, 1009, entitled METHOD OF PROGRAMMING A LIGHTING PRESETFROM A RADIO-FREQUENCY REMOTE CONTROL the entire disclosures of whichare hereby incorporated by reference.

The load control system 100 may comprise a plurality of occupancysensors 130, daylight sensors 140, and battery-powered remote controls150 for providing local control of the fluorescent lamps 104. Inaddition, the load control system 100 may comprise additional types ofinput devices as shown in FIG. 2A. The additional input devices of theload control system 100 may comprise a wall-mounted occupancy sensor250, a temperature sensor 252, a radiometer, a cloudy-day or shadowsensor, a humidity sensor, a pressure sensor, a smoke detector, a carbonmonoxide detector, an air-quality sensor, a security sensor, a proximitysensor, a fixture sensor, a wall-mounted keypad 254, a remote controlkeypad 255, a kinetic or solar-powered remote control, a key fob, a cellphone, a smart phone 256, a tablet 258, a personal digital assistant(PDA), a personal computer 259, a laptop, a timeclock, an audio-visualcontrol, safety devices (such as fire protection, water protection, andmedical emergency devices), a power monitoring device (such as a powermeter, an energy meter, a utility submeter, and a utility rate meter),or any residential, commercial, or industrial controller. In addition,the input devices may comprise one or more partition switches thattransmit RF signals in dependence upon whether a partition is opened orclosed. The input devices may further comprise a central controltransmitter to allow for central control of the fluorescent lamps 104.Specifically, the central control transmitter may be adapted to transmita digital message including one of: a timeclock command, a load shedcommand, a demand response command, a peak demand command, ortime-of-day pricing information. In addition, the digital ballastcontroller 120 could be operable to transmit information, such as thestatus and energy consumption of the controlled loads, back to thecentral control transmitter or one of the other input devices. One ormore of the different types of input devices may be provided in a singleload control system.

Alternatively, the input devices could comprise wired transmittersoperable to transmit control signals to the controller via a wiredcontrol link, for example, a digital communication link operating inaccordance with a predefined communication protocol (such as, forexample, one of Ethernet, IP, XML, Web Services, QS, DMX, BACnet,Modbus, LonWorks, and KNX protocols), a serial digital communicationlink, an RS-485 communication link, an RS-232 communication link, adigital addressable lighting interface (DALI) communication link, aLUTRON ECOSYSTEM communication link, or an analog control link. Inaddition, the wired transmitter could be adapted to produce one of aline-voltage control signal, a phase-control signal, a 0-10V controlsignal, and a contact closure output control signal.

Alternatively, the digital ballast controller 120 may comprise differentuser interfaces and form factors as shown in FIG. 2B. The user interfaceof the digital ballast controller 120 may not include the visualindicators 128 for providing feedback and may comprise different buttoncombinations than that shown in FIG. 2B. In addition, the user interfaceof the digital ballast controller 120 could also include a lens in thefront surface for directing infrared energy from an occupant to aninternal occupancy detection circuit (similar to that of the occupancysensor 130) for detecting occupancy and vacancy conditions. The digitalballast controller 120 may not include the user interface, but couldsimply comprise an in-wall device 260 adapted to be mounted inside anelectrical wallbox and to receive the RF signals from the wirelessoccupancy sensor 130, the wireless daylight sensor 140, and the wirelessbattery-powered remote control 150. In addition, the digital ballastcontroller 120 could alternatively be mounted to a ceiling, in anelectrical panel, to a DIN rail in an electrical closet (e.g., device262 in FIG. 2B), directly to a lighting fixture in which one of thedigital dimming ballasts 110 is installed, or to a junction box behind awall or above a ceiling (e.g., device 264 in FIG. 2B). The digitalballast controller 120 may also comprise a printed circuit board mountedin an enclosure or in a power panel, for example, as shown and describedin greater detail in commonly-assigned U.S. Pat. No. 5,808,417, issuedSep. 15, 1998, entitled LIGHTING CONTROL SYSTEM WITH CORRUGATED HEATSINK, the entire disclosure of which is hereby incorporated byreference. Further, the digital ballast controller 120 could comprise amulti-zone lighting control device 266, such as a GRAFIK EYE controlunit, which is adapted to be mounted in a multi-gang electrical wallboxand has an advanced user interface for configuring and adjusting thecontrolled lighting loads.

The ballasts 110 could alternatively be digital switching ballasts thatare only responsive to digital messages transmitted by the digitalballast controller 120 that include commands to turn the respectivelamps on and off. The digital switching ballasts would not be responsiveto commands to adjust the intensity of the respective lamp 104 acrossthe dimming range of the ballast, i.e., between the low-end intensityL_(LE) and the high-end intensity L_(HE). However, the digital switchingballasts may be operable to adjust the high-end intensity L_(HE) inresponse to digital messages received from the digital ballastcontroller 120.

In addition, the ballasts 110 could alternatively be digital bi-levelswitching ballasts that are each able to individually control (e.g.,turn off and on) a plurality of lamps (e.g., two or three lamps perballast). For example, a bi-level switching ballast controlling threelamps may be operable to turn all three lamps on to provide a maximumintensity, turn one lamp off and two lamps on to provide a first dimmedlevel, turn two lamps off and one lamp on to provide a second dimmerlevel (less than the first dimmed level), and turn all lamps off. Thedigital ballast controller 120 may transmit specific bi-level switchingcommands to the ballast 110 when the ballasts are bi-level switchingballasts (e.g., commands to turn on one lamp, turn of two lamps, etc.).Alternatively, a bi-level switching ballast may be responsive tocommands to adjust the intensity to any level across the dimming rangeof a standard dimming ballast, i.e., between the low-end intensityL_(LE) and the high-end intensity L_(HE). For example, the bi-levelswitching ballast may turn on all three lamps in response to receiving acommand to control the lamps to 100%, may turn on two lamps in responseto receiving a command to control the lamps to less than 100%, butgreater than or equal to 50%, may turn on one lamp in response toreceiving a command to control the lamps to less than 50%, but greaterthan 0%, and may turn off the lamps in response to receiving a commandto control the lamps to 0%. The bi-level switching ballasts providelower cost alternatives to standard dimming ballasts when only a fewdiscrete dimmed levels are required for an installation. For example, abi-level switching ballast may only turn one lamp of three lamps on inresponse to an occupancy sensor (e.g., the occupancy sensor 130)detecting an occupancy condition, and may turn on all lamps in responseto an actuation of a button of a remote control device (e.g., the remotecontrol device 150).

Further, the ballasts 110 could alternatively be emergency ballastshaving internal batteries for powering at least one lamp of a lightingfixture in the event of loss of power.

The load control system 100 of FIG. 1 could alternatively comprise loadcontrol devices for other types of electrical loads (rather thanballasts for fluorescent lamps). FIG. 2C shows examples of additionaltypes of electrical loads and load control devices that may be includedin the load control system 100. For example, the load control devices ofthe load control system 100 may also comprise a light-emitting diode(LED) driver 270 for driving an LED light source (i.e., an LED lightengine); a screw-in luminaire including a dimmer circuit and anincandescent or halogen lamp; a screw-in luminaire including a ballastand a compact fluorescent lamp; a screw-in luminaire including an LEDdriver and an LED light source; a dimming circuit for controlling theintensity of an incandescent lamp 272, a halogen lamp, an electroniclow-voltage lighting load, a magnetic low-voltage lighting load, oranother type of lighting load; an electronic switch, controllablecircuit breaker, or other switching device for turning electrical loadsor appliances on and off; a plug-in load control device 274,controllable electrical receptacle, or controllable power strip forcontrolling one or more plug-in electrical loads (such as coffee pots orspace heaters); a motor control unit for controlling a motor load, suchas a ceiling fan or an exhaust fan; a drive unit for controlling amotorized window treatment 276 or a projection screen; motorizedinterior or exterior shutters; a thermostat for a heating and/or coolingsystem; a temperature control device 278 for controlling a heating,ventilation, and air conditioning (HVAC) system; an air conditioner; acompressor; an electric baseboard heater controller; a controllabledamper; a humidity control unit; a dehumidifier; a water heater; a poolpump; a refrigerator; a freezer; a television or computer monitor; apower supply; an audio system or amplifier; a generator; an electriccharger, such as an electric vehicle charger; and an alternative energycontroller (e.g., a solar, wind, or thermal energy controller). Inaddition, a single digital ballast controller could be coupled tomultiple types of load control devices in a single load control system.

FIG. 3A is a simplified block diagram of a digital ballast controller200 (e.g., the digital ballast controller 120 of the load control system100 shown in FIG. 1). The electrical hardware of the digital ballastcontroller 200 is very similar to that of a standard dimmer switch. Thedigital ballast controller 200 comprises a hot terminal H and a neutralterminal N adapted to be coupled to the AC power source 102, and acontrol-hot terminal CH adapted to be coupled to one or more two-wiredigital dimming ballast (e.g., the two-wire digital dimming ballast 110of the load control system 100 shown in FIG. 1). The digital ballastcontroller 200 comprises a controllably conductive device (CCD) 210,i.e., a controlled switch, coupled in series electrical connectionbetween the AC power source 102 and the digital dimming ballasts 110 forgenerating a control-hot voltage V_(CH). The controllably conductivedevice 210 may comprise any suitable type of bidirectional semiconductorswitch, such as, for example, a triac, a field-effect transistor (FET)in a rectifier bridge, two FETs in anti-series connection, or one ormore insulated-gate bipolar junction transistors (IGBTs). Thecontrollably conductive device 210 is operable to conduct a total loadcurrent I_(LOAD) of the ballasts 110 and the lamps 104. The controllablyconductive device 210 includes a control input coupled to a drivecircuit 212. The digital ballast controller 200 further comprises amicroprocessor 214 coupled to the drive circuit 212 for rendering thecontrollably conductive device 210 conductive or non-conductive to thusgenerate the control-hot voltage V_(CH) at the control-hot terminal CH.The microprocessor 214 may alternatively comprise, for example, amicrocontroller, a programmable logic device (PLD), an applicationspecific integrated circuit (ASIC), a field-programmable gate array(FPGA), or any suitable processing device, controller, or controlcircuit.

The microprocessor 214 is coupled to a zero-crossing detector 216, whichis coupled between the hot terminal H and the neutral terminal N fordetermining the zero-crossings of the AC power source 102. Thezero-crossings are defined as the times at which the AC supply voltageof the AC power source 102 transitions from positive to negativepolarity, or from negative to positive polarity, for example, at thebeginning (and end) of each half-cycle. The microprocessor 214 may beoperable to measured a line-cycle time period T_(LC) by measuring the(i.e., the time period between every other zero-crossing of the AC powersource 102).

The microprocessor 214 provides the control inputs to the drive circuit212 at predetermined times relative to the zero-crossings of the ACpower source 102 for controlling the controllably conductive device 210to be non-conductive and conductive each half-cycle of the AC powersource to thus generate the control-hot voltage V_(CH). Specifically,the controllably conductive device 210 is controlled to benon-conductive at the beginning of each half-cycle and is renderedconductive at a firing time, such that the controllably conductivedevice is conductive for a conductive period each half-cycle of the ACpower source (i.e., the control-hot voltage V_(CH) resembles a forwardphase-control voltage). The microprocessor 214 is operable to adjust thefiring time of the controllably conductive device 210 across a smallrange each half-cycle to communicate the digital messages (i.e., packetsof digital data) to the digital dimming ballasts 110 as will bedescribed in greater detail below. In addition, if the lamps 104 of theboth ballasts 110 should be off, the microprocessor 214 may be operableto render the controllably conductive device 210 non-conductive for theentire length of each half-cycle to interrupt the load current I_(LOAD)to the ballasts, and thus, preventing the ballasts 110 from drawing anystandby current from the AC power source 102.

As mentioned above, the microprocessor 214 renders the controllablyconductive device 210 conductive each half-cycle to generate thecontrol-hot voltage V_(CH). The control-hot voltage V_(CH) ischaracterized by a frequency (e.g., approximately twice the frequency ofthe AC mains line voltage) that is much smaller the frequency of thedigital messages transmitted by the control devices of the prior artpower-line carrier communication systems. Since the controllablyconductive device 210 is coupled between the AC power source 102 and thedigital dimming ballasts 110, the control-hot voltage V_(CH) only existson the circuit wiring 114 between the digital ballast controller 120 andthe digital dimming ballasts 110 (i.e., the digital ballast controlleroperates to “swallow” the control-hot voltage V_(CH)). Accordingly, thecontrol-hot voltage V_(CH) does not interfere with other control devicesthat may be coupled to the AC power source 102. In addition, thecontrol-hot voltage V_(CH) is not degraded by a reactive element thatmay be coupled in parallel with the AC power source 102, for example, alarge capacitance due to the other control devices coupled in parallelwith the AC power source.

Since the electrical hardware of the digital ballast controller 200 isvery similar to that of a standard dimmer switch, the microprocessor 214could be controlled to alternately operate in a dimmer mode and adigital communication mode. In the dimmer mode, the microprocessor 214could render the controllably conductive device 210 conductive at aphase angle each half-cycle that is dependent upon the desired lightingintensity L_(DES) to control one or more prior art dimmable two-wireballasts, for example, a screw-in compact fluorescent lamp having anintegral dimmable electronic ballast circuit. In the digitalcommunication mode, the microprocessor 214 could render the controllablyconductive device 210 conductive each half-cycle to generate thecontrol-hot voltage V_(CH) to transmit digital messages to the digitaldimming ballasts 110 as described herein. Accordingly, the digitalballast controller 200 could be field-configurable to operate in thedimmer mode and the digital communication mode (e.g., using an advancedprogramming mode) depending upon the type of loads to which the digitalballast controller is coupled. An example of an advanced programmingmode for a wall-mounted load control device is described in greaterdetail in U.S. Pat. No. 7,190,125, issued Mar. 13, 2007, entitledPROGRAMMABLE WALLBOX DIMMER, the entire disclosure of which is herebyincorporated by reference.

The microprocessor 214 receives inputs from actuators, e.g., the toggleactuator 124 and the intensity adjustment actuator 126 of the digitalballast controller 120, and controls a visual display, e.g., the statusindicators 128 shown in FIG. 1. The microprocessor 214 is also coupledto a memory 218 for storage of the preset intensities of fluorescentlamps 104 and the serial number of wireless control devices (e.g.,wireless transmitters, such as the occupancy sensor 130, the daylightsensor 140, and the remote control 150) to which the digital ballastcontroller 200 is associated. The memory 218 may be implemented as anexternal integrated circuit (IC) or as an internal circuit of themicroprocessor 214. A power supply 220 is coupled between the hotterminal H and the neutral terminal H and generates a direct-current(DC) supply voltage V_(CC) for powering the microprocessor 214, thememory 218, and other low-voltage circuitry of the digital ballastcontroller 200.

The digital ballast controller 200 further comprises a wirelesscommunication circuit, e.g., an RF receiver 222 and an antenna 224 forreceiving the RF signals 106 from wireless control devices (i.e., theoccupancy sensor 130, the daylight sensor 140, and the remote control150). The microprocessor 214 is operable to control the controllablyconductive device 210 in response to the messages received via RFsignals (e.g., the RF signals 106). Examples of antennas forwall-mounted control devices, such as the digital ballast controller120, are described in greater detail in U.S. Pat. No. 5,982,103, issuedNov. 9, 1999, and U.S. Pat. No. 7,362,285, filed Apr. 22, 2008, bothentitled COMPACT RADIO FREQUENCY TRANSMITTING AND RECEIVING ANTENNA ANDCONTROL DEVICE EMPLOYING SAME, the entire disclosures of which arehereby incorporated by reference. Alternatively, the wirelesscommunication circuit could comprise an RF transmitter for transmittingRF signals, an RF transceiver for both receiving and transmitting RFsignals, or an infrared (IR) receiver for receiving IR signals. Thedigital ballast controller 200 could also include an integral occupancydetection circuit (not shown) similar to that of the occupancy sensor130 for detecting occupancy and vacancy conditions in the space in whichthe digital ballast controller 200 is located. The digital ballastcontroller 200 may comprise a lens in the front surface for receivinginfrared energy from an occupant in the space, for example, as shown incommonly-assigned U.S. Patent Application Publication No. 2010/0188009,published Jul. 29, 2010, entitled MULTI-MODAL LOAD CONTROL SYSTEM HAVINGOCCUPANCY SENSING, the entire disclosure of which is hereby incorporatedby reference.

FIG. 3B is a simplified block diagram of a digital dimming ballast 300(e.g., one of the digital dimming ballasts 110 of the load controlsystem 100 shown in FIG. 1) for controlling the intensity of afluorescent lamp 304. The ballast 300 comprises a control-hot terminalCH and a neutral terminal N that are adapted to be coupled to analternating-current (AC) power source (not shown) for receiving thecontrol-hot voltage V_(CH) from a digital ballast controller (e.g., thedigital ballast controllers 120, 200 shown in FIGS. 1 and 3A). Thedigital dimming ballast 300 comprises an RFI (radio frequencyinterference) filter circuit 310 for minimizing the noise provided onthe AC mains, and a rectifier circuit 320 for generating a rectifiedvoltage V_(RECT) from the control-hot voltage V_(CH). The digitaldimming ballast 300 may further comprises a boost converter 330 forgenerating a direct-current (DC) bus voltage V_(BUS) across a buscapacitor C_(BUS). The DC bus voltage V_(BUS) typically has a magnitude(e.g., approximately 465 V) that is greater than the peak magnitudeV_(PK) of the control-hot voltage V_(CH) (e.g., approximately 170 V).The boost converter 330 also operates as a power-factor correction (PFC)circuit for improving the power factor of the ballast 300. The digitaldimming ballast 300 also includes a load regulation circuit 340comprising an inverter circuit 342 for converting the DC bus voltageV_(BUS) to a high-frequency AC voltage V_(INV) and a resonant tankcircuit 344 for coupling the high-frequency AC voltage V_(INV) generatedby the inverter circuit to filaments of the lamp 304.

The digital dimming ballast 300 further comprises a microprocessor 360for controlling the intensity of the fluorescent lamp 304 to the desiredlighting intensity L_(DES) between the low-end intensity L_(EE) and thehigh-end intensity L_(HE). The microprocessor 360 may alternativelycomprise, for example, a microcontroller, a programmable logic device(PLD), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or any suitable processing device,controller, or control circuit. The microprocessor 360 is coupled to amemory 362 for storage of the control information of the digital dimmingballast 300. The digital dimming ballast 300 also comprises a powersupply 364, which receives the bus voltage V_(BUS) and generates a DCsupply voltage V_(CC) (e.g., approximately five volts) for powering themicroprocessor 360, the memory 362, and the other low-voltage circuitryof the ballast.

The microprocessor 360 provides a drive control signal V_(DRIVE) to theinverter circuit 342 for controlling the magnitude of a lamp voltageV_(L) generated across the fluorescent lamp 304 and a lamp current I_(L)conducted through the lamp. Accordingly, the microprocessor 360 isoperable to turn the fluorescent lamp 304 on and off and adjust (i.e.,dim) the intensity of the lamp. The microprocessor 360 receives a lampcurrent feedback signal V_(FB-IL), which is generated by a lamp currentmeasurement circuit 370 and is representative of the magnitude of thelamp current I_(L). The microprocessor 360 also receives a lamp voltagefeedback signal V_(FB-IL), which is generated by a lamp voltagemeasurement circuit 372 and is representative of the magnitude of thelamp voltage V_(L).

The ballast 300 comprises an edge detect circuit 380 for receiving therectified voltage V_(RECT) and generating an edge-detect control signalV_(ED) that is received by the microprocessor 360. For example, the edgedetect circuit 380 may drive the edge-detect control signal V_(ED) high(i.e., to approximately the DC supply voltage V_(CC)) when the magnitudeof the control-hot voltage V_(CH) rises above a rising thresholdV_(TH-R) (e.g., approximately 20 volts), and drives the edge-detectcontrol signal V_(ED) low when the magnitude of the control-hot voltageV_(CH) drops below a falling threshold V_(TH-F) (e.g., approximately 10volts). The microprocessor 360 is operable to determine the firing angleof the control-hot voltage V_(CH) each half-cycle of the AC power sourcein order to receive the digital messages transmitted by the digitalballast controller 120 as will be described in greater detail below.

The digital dimming ballast 300 could be controlled to alternatelyoperate in a dimmer mode and a digital communication mode. In the dimmermode, the ballast 300 may be operable to receive a standardphase-control signal from a prior-art dimmer switch and to determine thedesired lighting intensity L_(DES) for the lamp 304 in response to thelength of the conduction period of the phase-control voltage. In thedigital communication mode, the ballast 300 may be operable to receive acontrol-hot voltage V_(CH) from a digital ballast controller (e.g., thedigital ballast controllers 120, 200 shown in FIGS. 1 and 3A) and todetermine the desired lighting intensity L_(DES) in response to thedigital messages decoded from the control-hot voltage V_(CH).

The microprocessor 360 is operable to determine a control channel (oraddress) of the digital dimming ballast 300 in response to a channelsetting circuit, e.g., two or more DIP (dual in-line package) switches382. For example, four channels may be selected by adjusting thepositions of two DIP switches. Alternatively, the digital dimmingballast 300 could comprise rotary encoder or a plurality of jumpers forselecting the control channel. In addition, the control channel couldalternatively be selected in response to digital messages received fromthe digital ballast controller 120, 200 (e.g., automatically assignedusing a “soft-addressing” procedure or manually selected by a user via agraphical user interface running on a computer). The digital dimmingballast 300 may only be assigned to one control channel at a time.However, the digital dimming ballast 300 could alternatively be assignedto multiple control channels. In addition, the digital dimming ballast300 could alternatively comprise a different DIP switch for each of theplurality of types of wireless control devices to which the ballast maybe responsive (e.g., wireless transmitters, such as the occupancy sensor130, the daylight sensor 140, and the remote control 150 shown in FIG.1). The DIP switch for a specific type of wireless transmitter could beselected (by adjusting the position of the DIP switch) to enable controlof the digital dimming ballast 300 in response to that type of wirelesstransmitter.

The microprocessor 360 determines how the digital dimming ballast 300operates in response to the various inputs (i.e., the actuations of thetoggle actuator 124 and the intensity adjustment actuator 126 of thedigital ballast controller 120 or the RF signals 106 received from theoccupancy sensor 130, the daylight sensor 140, and the remote control150) in dependence upon the selected control channel an well as controlinformation stored in the memory 362. The control channel may determinewhich of the wireless control devices (i.e., the occupancy sensor 130,the daylight sensor 140, and the remote control 150) to which thedigital dimming ballast 300 is responsive. In addition, themicroprocessor 360 may determine if the digital dimming ballast 300should respond to actuations of the user interface of the digitalballast controller 120, 200 (e.g., the toggle actuator 124 and theintensity adjustment actuator 126) in response to the control channel.Since the digital dimming ballast 300 determines the control channel inresponse to the positions of the DIP switches 382 and the digitalballast controller 120 is associated with the wireless transmitters viaa manual procedure (i.e., pressing an actuator on the wirelesstransmitter and pressing an actuator on the digital ballast controller),a load control system including the digital dimming ballast 300 (e.g.,the load control system 100 shown in FIG. 1) requires no advancedcomputing device (e.g., a personal computer or laptop) to be programmedand configured after installation.

For example, the ballasts 110, 300 may respond to the various inputs independence upon the control channel as shown in the following table(i.e., which may be stored in the memory 362).

Channel Respond to . . . 1 User interface of digital ballast controllerOccupancy Sensors Remote Control #1 2 User interface of digital ballastcontroller Occupancy Sensors Daylight Sensors Remote Control #1 3 Userinterface of digital ballast controller Remote control #2 4 Userinterface of digital ballast controller Occupancy Sensors Remote Control#2When the digital ballast controller 120, 200 receives one of the variousinputs (i.e., the actuations of the toggle actuator 124 and theintensity adjustment actuator 126 or the RF signals 106 received fromthe occupancy sensor 130, the daylight sensor 140, and the remotecontrol 150), the digital ballast controller transmits digital messagesincluding information regarding the channels associated with the sourceof the control information to the digital dimming ballasts 110, 300. Forexample, if the digital ballast controller 120, 200 receives an occupiedcommand from the occupancy sensor 130, the digital ballast controllerwill include information regarding channels 1, 2, and 4 in the digitalmessage that is subsequently transmitted to the digital dimming ballasts110, 300.

The load control system 100 shown in FIG. 1 allows for easy retrofittingto upgrade from, for example, an older non-dim ballast system. Onceinstalled, the digital dimming ballasts 110, 300 are able to receivepower over the existing building wiring, and the digital ballastcontroller 120, 200 is able to transmit digital messages to the ballastsover the existing building wiring. In other words, the load controlsystem 100 requires no additional wiring and provides both power andcommunication over the two wires between the AC power source 102 and thedigital dimming ballasts 110, 300. The digital dimming ballasts 110, 300allow users of the system to control their visual environment, therebyimproving end user comfort and productivity. Since the load controlsystem 100 requires no additional wiring and no advanced computingdevice to be programmed, the load control system provides economicsavings in regards to installation and servicing, and provides acognitive benefit to those installing and servicing the load controlsystem. In addition, the digital dimming ballasts 110, 300 may be easilyreplaced in the event of a ballast failure since the control channel issimply determined from the positions of the DIP switches 382 (which maybe effortlessly adjusted to match the ballast that is being replaced).Further, the DIP switches 382 of a plurality of the ballasts 110, 300could be set at the time of manufacture and then shipped to a customer,such that a load control system including the plurality the digitaldimming ballast 110, 300 could be functional immediately uponinstallation.

FIG. 4A is a floor plan diagram of a first installation 160 of a loadcontrol system (e.g., the load control system 100) in a classroom 161.The classroom 161 has a presentation board 162 and a desk 164 at thefront end and three windows 166 at the back end. The classroom 161includes nine lighting fixtures 112A-112J, which each include arespective two-wire digital dimming ballast 110A-110J driving twofluorescent lamps 104. A digital ballast controller 120A (e.g., thedigital ballast controller 120, 200 shown in FIGS. 1 and 3A) is mountedin an electrical wallbox adjacent the presentation board 162 and iselectrically coupled to the ballasts 110A-110J via a circuit wiring 114Afor coupling a control-hot voltage V_(CH) generated by the digitaldimming ballast 120A and the neutral side of an AC power source to eachballast. An occupancy sensor 130A and a daylight sensor 140A are mountedto the ceiling of the classroom 161 near the center of the room, and tworemote controls 150A, 150B are located on the desk 164.

For example, the digital dimming ballasts 110A-110J could replacestandard non-dim ballasts, and the digital ballast controller 120A couldreplace a standard mechanical switch. The digital ballast controller120A is able to control ballasts 110A-110J in groups, for example,depending upon the distance of the fixtures 112A-112J from the front endor the back end of the classroom 161. According to the exampleinstallation of FIG. 4A, all of the ballasts 110A-110J in the classroom161 are responsive to actuations of the user interfaces of the digitalballast controller 120A. Only the ballasts 110C, 110F, 110J closest tothe windows 166 adjust the intensities of the controlled fluorescentlamps 104 in response to the daylight sensor 140A. The ballasts 110A,110D, 110G closest to the presentation board 162 are controlled by thesecond remote control 150B, while the remaining ballasts 110B, 110C,110E, 110F, 110H, 110J are controlled by the occupancy sensor 130A andthe first remote control 150A.

To provide this functionality, the ballasts 110A, 110D, 110G in a firstgroup 170 closest to the presentation board 162 are assigned controlchannel 3, the ballasts 110B, 110E, 110H in a second group 172 in thecenter of the room are assigned control channel 1, and the ballasts110C, 110F, 110J in a third group 174 closest to the windows 166 areassigned control channel 2 (as detailed in the table shown above).Therefore, the ballasts 110A, 110D, 110G in the first group 170 respondto the user interfaces of the respective digital ballast controller 120Aand the second remote control 150B. The ballasts 110B, 110E, 110H in thesecond group 172 respond to the user interfaces of the respectivedigital ballast controllers 120A-120C, the occupancy sensor 130A, andthe first remote control 150A. The ballasts 110C, 110F, 110J in thethird group 174 respond to the user interfaces of the respective digitalballast controller 120A, the occupancy sensor 130A, the daylight sensor140A, and the first remote control 150A.

If all of the lamps 104 controlled by the digital dimming ballasts110A-110J on the circuit wiring 114A should be off, the digital ballastcontroller 120A can render the controllably conductive device 210non-conductive to disconnect the ballasts from the AC power source, andthus prevent the ballasts from drawing any standby current from the ACpower source. In addition, one or more of the ballasts 110A-110J couldcomprise prior art non-dim ballasts that would not be responsive to anydigital messages transmitted by the digital ballast controller 120A tothe digital dimming ballasts in the classroom 161. The non-dim ballastswould each simply remain at the high-end intensity L_(HE) while thedigital dimming ballasts are controlled through the dimming range by thedigital ballast controller 120A. The digital ballast controller 120Acould turn off the non-dim ballasts (as well as the digital dimmingballasts) by rendering the controllably conductive device 210non-conductive. As previously mentioned, the ballasts couldalternatively comprise digital switching ballasts that are responsive todigital messages transmitted by the digital ballast controller 120A, butonly to commands to turn the respective lamps on and off.

FIG. 4B is a floor plan diagram of a second example installation 160′ ofa load control system (e.g., the load control system 100) in a classroom161′. The classroom 161′ of FIG. 4B includes three different circuitwirings 114A, 114B, 114C providing power to the ballasts 110A-110J, andthus three digital ballast controllers 120A, 120B, 120C, which aremounted in electrical wallboxes adjacent a presentation board 162′. Thefirst three ballasts 110A, 110B, 110C are electrically coupled to thefirst digital ballast controller 120A via the first circuit wiring 114A.In addition, ballasts 110D, 110E, 110F are electrically coupled to thesecond digital ballast controller 120B via the second circuit wiring114B, and ballasts 110G, 110H, 110J are electrically coupled to thethird digital ballast controller 120C via the third circuit wiring 114C.

The digital ballast controllers 120A, 120B, 120C of FIG. 4B are able tocontrol the ballasts 110A-110J in three groups 170′, 172′, 174′, i.e.,depending upon the distance of the fixtures 112A-112J from the front endor the back end of the classroom 161′. Accordingly, the digital ballastcontrollers 120A, 120B, 120C are able to control the ballasts 110A-110Jin response to an occupancy sensor 130B, a daylight sensor 140A, andremote controls 150A, 150B independent of the specific circuit wirings114A, 114B, 114C that extend from the front end to the back end of theclassroom 161′ (i.e., perpendicular to the groups 170′, 172′, 174′). Allof the ballasts 110A-110J in the classroom 161′ are responsive toactuations of the user interfaces of the respective digital ballastcontrollers 120A-120C. Only the ballasts 110C, 110F, 110J closest towindows 166′ adjust the intensities of the controlled fluorescent lamps104 in response to the daylight sensor 140A. The ballasts 110A, 110D,110G closest to the presentation board 162′ are controlled by the secondremote control 150B, while the remaining ballasts 110B, 110C, 110E,110F, 110H, 110J are controlled by the occupancy sensor 130A and thefirst remote control 150A.

Since each of the digital ballast controllers 120A, 120B, 120C operatesto swallow the digital messages transmitted to the ballasts 110A-110J onthe respective circuit wirings 114A, 114B, 114C, these digital messagesare not received the other digital ballast controllers and thus do notinterfere with the other digital ballast controllers. However, each ofthe digital ballast controllers 120A, 120B, 120C may be operable totransmit digital messages to the other digital ballast controllers viaRF signals. Specifically, the digital ballast controller 120A, 120B,120C may be operable to transmit digital messages to the other digitalballast controllers in response to actuations of the user interfaces,such that all of the ballasts 110A-110J in the classrooms 161, 161′ maybe responsive to actuations of the user interfaces of any of the digitalballast controllers.

If the digital dimming ballasts 110, 300 are replacing non-dim ballasts,the sockets for the controlled lamps may need to be upgraded fromnon-dim sockets to dimmable sockets. However, if new ballasts aredigital switching ballasts or digital bi-level switching ballasts, thesockets do not need to be upgraded to dimmable sockets. The load controlsystem 100 can still provide group control of the digital switchingand/or digital bi-level switching ballasts independent of the circuitwiring (e.g., circuit wirings 114A, 114B, 114C), as well as provide afew discrete dimmed levels of the digital bi-level switching ballasts.

FIG. 5 is a simplified perspective view of a retrofit kit 180 having atwo-wire digital dimming ballast 110′ (e.g., one of the two-wireddigital dimming ballast 110 of the load control system 100 of FIG. 1)mounted to a pan 182, which is designed to be easily installed in alighting fixture. The retrofit kit 180 further comprises two pairs ofdimmable lamp sockets 184 that are mounted to the pan 182 and arepre-wired to the digital dimming ballast 110′ via electrical wires 185.Each pair of sockets 184 is operable to be coupled to, for example, aU-bend fluorescent lamp as shown in FIG. 5. Alternatively, the sockets184 could be mounted at opposite ends of the pan 182 to thus be adaptedto be coupled to a straight fluorescent lamp. In addition, the retrofitkit 180 could comprise more or less sockets 184 to allow the ballast110′ to be coupled to a different number of lamps. The retrofit kit 180further comprises a control-hot electrical wire 186 and a neutralelectrical wire 188 for coupling the ballast 110′ to the circuit wiringof the building. Accordingly, to provide for easy retrofit installation,the retrofit kit 180 may be assembled prior to shipment to a customer.The old pan of the ballast being replaced can simply be removed from alighting fixture and the new retrofit kit 180 can be installed into thelighting fixture its place with the only required electrical connectionsbeing the control-hot electrical wire 186 and the neutral electricalwire 188 to the circuit wiring of the building.

FIGS. 6A and 6B are a simple timing diagrams of a control-hot voltageV_(CH) (e.g., the control-hot voltage generated by the digital ballastcontroller 120 of FIG. 1) showing a data pattern of a transmitteddigital message. As previously mentioned, the digital ballast controller120 may be operable to adjust the firing time of the respectivecontrollably conductive device 210 across a small time window T_(WIN)(e.g., approximately 300 microseconds) each line cycle to communicatethe digital messages to the respective digital dimming ballasts 110.Digital information (i.e., bits of the transmitted digital messages) isencoded in the firing times of timing edges (i.e., transitions) of thecontrol-hot voltage V_(CH). Specifically, the bits of the transmitteddigital messages are encoded in the firing time of a data edge (i.e., adata edge time) of the controllably conductive device 210 as measuredwith respect to a firing time of a reference edge (i.e., a referenceedge time) in a previous half-cycle. In other words, the bits of thetransmitted digital messages are encoded as a function of the firingtimes of the reference and data edges. Each data pattern includes ahalf-cycle having a reference edge and a number N_(DP) of subsequenthalf-cycles having data edges. Each reference edge is spaced at areference edge time period T_(REF) (e.g., approximately 1.3milliseconds) from the zero-crossing of the present half-cycle. As shownin FIG. 6B, there is one data edge for each reference edge (i.e., thenumber N_(DP) of half-cycles having data edges equal one). When thecontrollably conductive device of the digital ballast controller 120comprises a FET in a rectifier bridge, two FETs in anti-seriesconnection, or one or more insulated-gate bipolar junction transistors(IGBTs), the digital ballast controller may be operable to control thelength of a transition times (i.e., the rising or falling times) of thereference edges and the data edges.

The value of the digital data transmitted by the digital ballastcontroller 120 is dependent upon an offset time period T_(OS) (i.e., adifference) between the data edge and the previous reference edge (i.e.,in the previous half-cycle). The digital ballast controller 120 maycontrol the data edges to be at one of four times across the time windowT_(WIN), thus resulting in one of four offset time periods T_(OS1),T_(OS2), T_(OS3), T_(OS4), from the previous reference edge, such thattwo bits may be transmitted each line cycle. To transmit bits “00”, thedigital ballast controller 120 is operable to render the controllablyconductive device 210 conductive at the first possible data edge time,such that the first offset time period T_(OS1) (e.g., approximately 8.33milliseconds) exists between the reference edge and the data edge. Forexample, each of the possible data edge times may be an offset perioddifference ΔT_(OS) (e.g., approximately 100 microseconds) apart, and therise time of the control-hot voltage V_(CH) at the data edges is lessthan approximately 10 microseconds.

Accordingly, the digital ballast controller 120 is operable to controlthe offset time period T_(OS) between the reference edge and the dataedge to the second offset time period T_(OS2) (e.g., approximately 8.43milliseconds) to transmit bits “01”, to the third offset time periodT_(OS3) (e.g., approximately 8.53 milliseconds) to transmit bits “10”,and the fourth offset time period T_(OS4) (e.g., approximately 8.63milliseconds) to transmit bits “11” as shown in FIG. 6. Themicroprocessor 360 of each digital ballast 110 determines if the offsettime period T_(OS) of each data pattern is approximately equal to one ofthe four offset time periods T_(OS1), T_(OS2), T_(OS3), T_(OS4) within adefault tolerance ΔT_(OS), which may be equal to, for example,approximately fifty microseconds. Alternatively, the number of dataedges possible in the time window T_(WIN) could be greater than four,for example, eight in order to transmit three bits of data each linecycle.

When the digital ballast controller 120 is not transmitting a digitalmessage to the digital dimming ballasts 110, the digital ballastcontroller continues to render the controllably conductive device 210conductive as if the digital ballast controller was continuouslytransmitting bits “00.” Specifically, the digital ballast controller 120renders the controllably conductive device 210 conductive after thereference edge time period T_(REF) from the zero-crossing in a firsthalf-cycle of each line cycle and renders the controllably conductivedevice conductive after the first offset time period T_(OS1) in theother half-cycle of the line cycle as measured from the end of thereference edge time period T_(REF) in the previous half-cycle, such thatthe control-hot voltage V_(CH) generated by the digital ballastcontroller has at least one timing edge in each half-cycle of the ACpower source 102. Because the control-hot voltage V_(CH) has at leastone timing edge in each half-cycle, the digital dimming ballasts 110 donot have zero-crossing detectors having low voltage thresholds that maybe susceptible to noise on the AC mains line voltage, thus causingcommunication reception errors. Rather, the digital dimming ballasts 110include the edge detect circuit 380 having the rising threshold V_(TH-R)(i.e., approximately 20 volts), which is large enough, such that thedigital dimming ballasts 110 has an enhance noise immunity to typicalnoise on the AC mains line voltage.

Alternatively, the digital ballast controller 120 could render thecontrollably conductive device 210 fully conductive (i.e., forapproximately the length of each half-cycle) when the digital ballastcontroller is not transmitting a digital message (i.e., the control-hotvoltage V_(CH) is a full-conduction waveform), Accordingly, thecontrol-hot voltage V_(CH) does not have at least one timing edge ineach half-cycle when the digital ballast controller is not transmittinga digital message to the digital dimming ballasts 110.

Alternatively, the digital dimming ballasts 110 may be operable to becontrolled into an emergency mode in which the ballasts each control theintensity of the respective lamp 104 to the high-end intensity L_(HE).For example, a normally-open bypass switch could be coupled in parallelwith the digital ballast controller 120 and could be rendered conductiveduring an emergency condition, such that a full-conductive waveform isprovided to the control-hot terminals CH of the digital dimming ballasts110. The digital dimming ballasts 110 could each be operable to controlthe intensity of the respective lamp 104 to the high-end intensitiesL_(HE) in response to receiving the full-conduction waveform at thecontrol-hot terminal CH.

FIG. 7 is a simple diagram of a message structure for a digital messagetransmitted by a digital ballast controller (e.g., the digital ballastcontroller 120 of the load control system shown in FIG. 1). Each digitalmessage comprises a total number N_(DM) of bits (e.g., 20 bits). Thefirst four bits comprises a start pattern, which includes a unique startsymbol as will be described in greater detail below with reference toFIG. 8. A channel mask of each digital message includes four bits, eachof which may be set to indicate the channels of the ballasts 110 thatshould respond to the digital message. For example, if the ballasts 110that have control channel 1 should respond to the digital message, thefirst bit of the channel mask will be a logic one value. The channelmask is followed by two bits that determine a command type of thedigital message and five bits that include an intensity level for thefluorescent lamps 104 or data for the ballasts 110. Finally, eachdigital message concludes with five bits that are used to determine ifan error occurred during transmission and reception of the digitalmessage (e.g., a checksum). Accordingly, each digital messagestransmitted by the ballast controller 120 is transmitted across apredetermined (i.e., fixed) number of consecutive line cycles, e.g., tenline cycles.

FIG. 8 is a simple timing diagram of a control-hot voltage V_(CH)showing a start pattern used to start a digital message transmitted by adigital ballast controller (e.g., the digital ballast controller 120 ofthe load control system shown in FIG. 1). To transmit the start pattern,the digital ballast controller 120 transmits bits “00” during a firstline cycle and then transmits the unique start symbol during a secondsubsequent line cycle by rendering the controllably conductive device210 conductive after a start symbol time period T_(START) after thereference edge in the previous half-cycle. The start symbol time periodT_(START) is unique from the offset time periods T_(OS1)-T_(OS4) used totransmit data to the digital dimming ballasts 110 and may be longer thanthe offset times, for example, approximately 8.73 milliseconds.

The ballasts 110 continuously monitor the control-hot voltage V_(CH) todetermine if the digital ballast controller has transmitted a startpattern including the unique start symbol. Specifically, themicroprocessor 360 of each digital dimming ballast 110 measures timeperiods T_(RE) between the rising edges in each consecutive half-cycleand stores these times in the memory 362. The microprocessor 360 looksfor three consecutive measured time periods T₁, T₂, T₃ stored in thememory 362 that have values corresponding to the start pattern as shownin FIG. 8, i.e.,

T ₁ =T _(OS1),

T ₂ =T _(LC) −T _(OS1), and

T ₃ =T _(START),

where T_(LC) is the line-cycle time period, which represents the lengthof each line cycle of the AC power source 102. As mentioned above, theline-cycle time T_(LC) period is measured by the microprocessor 360(i.e., the time period between every other zero-crossing of the AC powersource 102). Alternatively, the line-cycle time T_(LC) period may be afixed value stored in the memory 362 (e.g., approximately 16.66milliseconds). Because the start symbol time period T_(START) is uniquefrom the offset time periods T_(OS1)-T_(OS4) used to transmit data tothe digital dimming ballasts 110, the digital ballast controller 120 isable to interrupt a first digital message that is being transmitted inorder to transmit a second digital message to the ballasts 110 bytransmitting the start symbol before the end of the first digitalmessage.

Since the second time period T₂ of the three consecutive measured timeperiods is a function of the line-cycle time period T_(LC), which mayvary depending upon characteristics the load control system 100 that arenot controlled by the digital ballast controller 120, the microprocessor360 determines if the second time period T₂ is equal to the line-cycletime period T_(LC) minus the first offset time period T_(OS1) within awidened tolerance ΔT_(OS-W), which is greater than the default toleranceΔT_(OS), for example, approximately 100 microseconds. Because thedigital ballast controller 120 requires four half-cycles to transmit thestart pattern, the start pattern takes up 4 bits of each digital messageas shown in FIG. 7. After transmitting the start pattern, the digitalballast controller 120 is operable to immediately begin transmittingdata in the next line cycle by generating a reference edge in the nexthalf-cycle and a data edge in the subsequent half-cycle as shown in FIG.8.

FIGS. 9-13 show example flowcharts executed by a control circuit of adigital ballast controller (e.g., the microprocessor 214 of the digitalballast controller 120, 200). Specifically, FIG. 9 is a simplifiedflowchart of a button procedure 400 executed by the microprocessor 214of the digital ballast controller 120 in response to an actuation of oneof the actuators of the user interface at step 410 in, for example, theexample installations 160, 160′ of FIGS. 4A and 4B. The microprocessor214 uses a transmit (TX) buffer to store digital messages to transmit tothe digital dimming ballasts 110. If the toggle actuator 124 wasactuated at step 412, the microprocessor 214 loads a digital messagehaving a toggle command into the TX buffer at step 414, and sets thechannel mask of the digital message equal to “1111” at step 416. Themicroprocessor 214 then sets a TX Flag to indicate that the digitalballast controller 120 is presently transmitting a digital message tothe digital dimming ballasts 110 at step 418, before the buttonprocedure 400 exits. Accordingly, all of the digital dimming ballasts110 will toggle the controlled lamps 104 (from off to on or from on tooff) in response to receiving the transmitted digital message.

If the toggle actuator 124 was not actuated at step 412, but theintensity adjustment actuator 126 was actuated at step 418, themicroprocessor 214 determines if the upper portion 126A or the lowerportion 126B of the intensity adjustment actuator was just pressed orreleased. If the upper portion 126A of the intensity adjustment actuator126 was pressed at step 420, the microprocessor 214 loads a digitalmessage having a start raise command into the TX buffer at step 422, andsets the channel mask of the digital message equal to “1111” at step 416before the button procedure 400 exits. If the upper portion 126A of theintensity adjustment actuator 126 was released at step 424, themicroprocessor 214 loads a digital message having a stop raise commandinto the TX buffer at step 426. If the lower portion 126B of theintensity adjustment actuator 126 was pressed at step 428, themicroprocessor 214 loads a digital message having a start lower commandinto the TX buffer at step 430. If the lower portion 126B of theintensity adjustment actuator 126 was released at step 432, themicroprocessor 214 loads a digital message having a stop lower commandinto the TX buffer at step 434.

FIGS. 10A and 10B are simplified flowcharts of an RF message procedure500 executed by the microprocessor 214 of the digital ballast controller120 when digital message is received from one of the occupancy sensor130, the daylight sensor 140, and the remote control 150 via the RFsignals 106 at step 510. If the received digital message is from theoccupancy sensor 130 at step 512 and includes an occupied command atstep 514, the microprocessor 214 loads a digital message having an oncommand into the TX buffer at step 516, sets the channel mask of thedigital message equal to “1101” at step 518, and sets the TX Flag atstep 520, before the RF message procedure 500 exits. If the receiveddigital message includes a vacant command at step 522, themicroprocessor 214 loads a digital message having an off command intothe TX buffer at step 524, sets the channel mask equal to “1101” at step518, and sets the TX Flag at step 520. If the received digital messageis not from the occupancy sensor 130 at step 512, but is from thedaylight sensor 140 at step 526, the microprocessor 214 loads a digitalmessage including the total light intensity L_(T-SNSR) measured by thedaylight sensor 140 into the TX buffer at step 528, sets the channelmask equal to “0100” at step 530, and sets the TX Flag at step 520,before the RF message procedure 500 exits.

Referring to FIG. 10B, if the received digital message is from one ofthe remote controls 150A, 150B at step 532 and the on button 152 wasactuated at step 534, the microprocessor 214 loads a digital messagehaving an on command into the TX buffer at step 536. If the receiveddigital message is from the first remote control 150A at step 538, themicroprocessor 214 sets the channel mask of the digital message in theTX buffer equal to “1100” at step 540. The microprocessor 214 then setsthe TX Flag at step 541 to indicate that the digital ballast controller120 is presently transmitting and the RF message procedure 500 exits.However, if the received digital message is from the second remotecontrol 150B at step 538, the microprocessor 214 sets the channel maskof the digital message equal to “0011” at step 542 and sets the TX Flagat step 541, before the RF message procedure 500 exits. If the offbutton 154 was actuated at step 544, the microprocessor 214 loads adigital message having an off command into the TX buffer at step 546,before setting the channel mask to either “1100” or “0011” at steps 540,542, respectively, and setting the TX Flag at step 541.

If the raise button 155 was just pressed at step 548, the microprocessor214 loads a digital message having a start raise command into the TXbuffer at step 550. If the raise button 155 was released at step 552,the microprocessor 214 loads a digital message having a stop raisecommand into the TX buffer at step 554. If the lower button 156 was justpressed at step 556, the microprocessor 214 loads a digital messagehaving a start lower command into the TX buffer at step 558. If thelower button 156 was released at step 560, the microprocessor 214 loadsa digital message having a stop lower command into the TX buffer at step562. Finally, if the preset button 158 was pressed at step 564, themicroprocessor 214 loads a digital message having a preset command intothe TX buffer at step 566, before the microprocessor sets the channelmask at steps 540, 542 and sets the TX Flag at step 541, and the RFmessage procedure 500 exits.

FIG. 11 is a simplified flowchart of a zero-crossing procedure 600executed by the microprocessor 214 of each digital ballast controller120 periodically, e.g., once every half-cycle at the zero-crossing ofthe present half-cycle as determined from the zero-crossing detector 216at step 610. The microprocessor 214 uses a timer that is alwaysincreasing in value with respect to time to determine when to render thecontrollably conductive device 210 conductive to generate the referenceedges and the data edges. First, the microprocessor 214 updates theline-cycle time period T_(LC) (for example, by measuring the time periodbetween every other zero-crossing) at step 611.

The microprocessor 214 uses a variable m to keep track of whether thenext rising edge of the control-hot voltage V_(CH) is a reference edge(e.g., if the variable m equals zero) or a data edge (e.g., if thevariable m equals one). If the variable m is equal to zero at step 612at the present zero-crossing (i.e., the digital ballast controller 120should generate a reference edge during the present half-cycle), themicroprocessor 214 sets a timer interrupt for an interrupt time equal toa present value t_(TIMER) of the timer plus the reference edge timeperiod T_(REF) at step 614. When the value t_(TIMER) of the timerreaches the set interrupt time for the timer interrupt, themicroprocessor 214 will render the controllably conductive device 210conductive during a timer interrupt procedure 700, which will bedescribed in greater detail below with reference to FIG. 12. If thevariable m is equal to one at step 612 (i.e., the digital ballastcontroller 120 should generate a data edge during the presenthalf-cycle), the zero-crossing procedure 600 simply exits.

FIG. 12 is a simplified flowchart of the timer interrupt procedure 700that is executed by the microprocessor 214 of each digital ballastcontroller 120 to generate the reference and data edges of thetransmitted digital messages. The microprocessor 214 executes the timerinterrupt procedure 700 when the value of the timer equals the setinterrupt time at step 710, for example, as set during the zero-crossingprocedure 600. The microprocessor 214 first renders the controllablyconductive device 210 conductive at step 712. If the variable m is equalto zero at step 714 (i.e., a reference edge was generated at step 712),the microprocessor 214 sets a base time t₀ equal to the present value ofthe timer (i.e., the time at which the reference edge was generated) atstep 716. The microprocessor 214 then prepares to generate a data edgein the next half-cycle by setting the variable m to one at step 718 andexecuting a data edge procedure 800, which will be described in greaterdetail below with reference to FIG. 13. The microprocessor 214 uses thebase time t₀ of the reference edge during the data edge procedure 800 toaccurately set up a timer interrupt for generating the data edge in thenext half-cycle.

If the microprocessor 214 has not reached the end of the present forwarddigital message at step 720, the microprocessor determines if there is ahigher priority message to transmit at step 722. If the microprocessor214 does not have a higher priority message to transmit and should notinterrupt the forward digital message that is presently beingtransmitted at step 722, the timer interrupt procedure 700 simply exits.However, if the microprocessor 214 should interrupt the digital messagepresently being transmitted at step 722, the microprocessor clears thelast digital message out of the TX buffer at step 724, before the timerinterrupt procedure 700 exits. If the microprocessor 214 has reached theend of the present forward digital message at step 720, themicroprocessor clears the last message from the TX buffer at step 726.If there are more forward digital messages to transmit in the TX bufferat step 728, the timer interrupt procedure 700 simply exits. However, ifthere are not more forward digital messages to transmit at step 728, themicroprocessor 214 clears the TX Flag at step 730, before the timerinterrupt procedure 700 exits.

If the variable m is equal to one at step 714 (i.e., a data edge wasgenerated at step 712), the microprocessor 214 sets the variable m tozero at step 732 and the timer interrupt procedure 700 exits, such thatthe microprocessor will generate a reference edge during the nexthalf-cycle.

FIG. 13 is a simplified flowchart of the data edge procedure 800, whichis executed during the timer interrupt procedure 700 in order to set upa timer interrupt to generate the data edges of the control-hot voltageV_(CH). If the microprocessor 214 is not presently transmitting adigital message to the digital dimming ballasts 110 at step 810, themicroprocessor sets the interrupt time of the next timer interrupt equalto the base time t₀ (as determined at step 716 of the timer interruptprocedure 700) plus the first offset time period T_(OS1) at step 812,before the data edge procedure 800 exits. The microprocessor 214continues to render the controllably conductive device 210 conductive asif the microprocessor was continuously transmitting bits “00” while themicroprocessor is not transmitting digital messages to the digitaldimming ballasts 110 (i.e., the load control system 100 is in an idlestate).

If the microprocessor 214 is transmitting a digital message to thedigital dimming ballasts 110 at step 810, the microprocessor 214determines if a start pattern is presently being transmitted at step814. If the microprocessor 214 is presently transmitting a start patternat step 814, the microprocessor 214 generates the start pattern at step816. For example, if the microprocessor 214 is presently transmittingthe first two bits of the start pattern, the microprocessor 214 sets theinterrupt time of the next timer interrupt equal to the base time t₀plus the first offset time period T_(OS1) at step 816 and the data edgeprocedure 800 exits. If the microprocessor 214 is presently transmittingthe last bit of the start pattern, the microprocessor 214 sets a timerinterrupt for the interrupt time of the next timer interrupt equal tothe base time t₀ plus the start symbol time period T_(START) at step 816and sets a variable n to one at step 820, before the data edge procedure800 exits. The microprocessor 214 uses the variable n to keep track ofwhich bits of the present digital message in the TX buffer are presentlybeing transmitted, where a value of one for the variable n representsthe first bit and a value equal to the total number N_(DM) of bits ofthe digital message represents the last bit of the digital message.

If the microprocessor 214 is transmitting a digital message to thedigital dimming ballasts 110 at step 810, but is not transmitting astart symbol at step 814, the microprocessor transmits the data patternsof the digital message. If the next two bits TX[n+1,n] of the digitalmessage in the TX buffer are equal to “00” at step 822, themicroprocessor 214 sets the interrupt time of the next timer interruptequal to the base time t₀ plus the first offset time period T_(OS1) atstep 824. If the next two bits TX[n+1,n] of the digital message in theTX buffer are equal to “01” at step 826, equal to “10” at step 830, orequal to “11” at step 834, the microprocessor 214 sets the interrupttime of the next timer interrupt equal to the base time t₀ plus thesecond offset time period T_(OS2) at step 828, the base time t₀ plus thethird offset time period T_(OS3) at step 832, or the base time t₀ plusthe fourth offset time period T_(OS4) at step 836, respectively.

If the variable n is not equal to the total number N_(DM) of bits of thedigital message minus one at step 838, the microprocessor 214 increasesthe variable n by two at step 840 (since two bits are transmitted eachline cycle). If the variable n is equal to the total number N_(DM) ofbits of the digital message minus one at step 838 (i.e., the presentdigital message is complete), the data edge procedure 800 simply exits.

FIGS. 14 and 15 show example flowcharts executed by a control circuit ofa digital dimming ballast (e.g., the microprocessor 360 of one of thedigital dimming ballasts 110, 300) to receive digital messagestransmitted by a digital ballast controller (e.g., the digital ballastcontroller 120, 200). Specifically, FIG. 14 is a simplified flowchart ofa receiving procedure 900 executed by the microprocessor 360 of eachdigital dimming ballast 110 periodically (e.g., once every half-cycle)to receive the digital messages transmitted by the connected digitalballast controller 120. Specifically, the transmission procedure 900 isexecuted when a rising edge of the control-hot voltage V_(HC) (i.e., areference edge or a data edge) is detected at step 910 (i.e., inresponse to the edge-detect control signal V_(ED) generated by the edgedetect circuit 380). The microprocessor 360 uses a receive (RX) bufferto store the bits of the digital messages as they are being received, sothat the digital message can be stored until the microprocessorprocesses the messages to thus control the fluorescent lamps 104.

As previously mentioned, the microprocessor 360 continually monitors thecontrol-hot voltage V_(CH) to determine if the digital ballastcontroller 120 has transmitted a start pattern including the uniquestart symbol by measuring the time period between the times of therising edges in each consecutive half-cycle and storing these timeperiods in the memory 362. Specifically, the microprocessor 360 sets arising edge time t_(E) equal to the present value t_(TIMER) of the timerat step 912, and then determines the last three time periods T₁, T₂, T₃between the rising edges of the control-hot voltage V_(CH) at step 914by setting the first time period T₁ equal to the previous second timeperiod T₂, setting the second time period T₂ equal to the previous thirdtime period T₃, and setting the third time period T₃ equal to the risingedge time t_(E) minus a previous rising edge time t_(E-PREV).

Next, the microprocessor 360 determines if the last three time periodsT₁, T₂, T₃ between the rising edges of the control-hot voltage V_(CH)are approximately equal to time periods T_(OS1), T_(LC)−T_(OS1), andT_(START), respectively. At step 916, the microprocessor 360 determinesif the first period T₁ is equal to the first offset time period T_(OS1)within the default tolerance ΔT_(OS), i.e.,

if (T _(OS1) −ΔT _(OS))<T ₁≦(T _(OS1) +ΔT _(OS)).

At step 918, the microprocessor 360 determines if the second period T₂is equal to the line cycle period T_(LC) minus the first offset timeperiod T_(OS1) within the widened tolerance ΔT_(OS-W), i.e.,

if ([T _(LC) −T _(OS1) ]−ΔT _(OS-W))<T ₂≦([T _(LC) −T _(OS1) ]+ΔT_(OS-W)).

At step 920, the microprocessor 360 determines if the third period T₃ isequal to the start symbol offset time period T_(START) within thedefault tolerance ΔT_(OS), i.e.,

if (T _(START) −ΔT _(OS))<T ₃≦(T _(START) +ΔT _(OS)).

If a start pattern was not received at step 916, 918, 920, themicroprocessor 360 sets the previous rising edge time t_(E-PREV) equalto the present rising edge time t_(E) at step 922. If the microprocessor360 is not presently receiving a digital message at step 924, thereceiving procedure 900 simply exits. If the microprocessor 360 receiveda start pattern at step 918, 920, 922, the microprocessor gets ready toreceive the data patterns of the digital message by clearing the RXbuffer at step 926 and setting a variable x to zero at step 928, beforethe receiving procedure 900 exits. The microprocessor 360 uses thevariable x to keep track of whether the next received edge will be areference edge (i.e., if the variable x is equal to zero) or a data edge(i.e., if the variable x is equal to one). Accordingly, themicroprocessor 360 will expect a reference edge during the nexthalf-cycle after setting the variable x equal to zero at step 928.

If the microprocessor 360 is presently receiving a digital message atstep 924 and the variable x equals zero at step 930, the microprocessor360 determines that the rising edge that was just received at step 910is a reference edge of a data pattern. Specifically, the microprocessor360 sets a reference edge time t_(REF-E) equal to the rising edge timet_(E) (from step 912) at step 932 and sets the variable x equal to oneat step 934, before the receiving procedure 900 exits. If themicroprocessor 360 is presently receiving a digital message at step 912and the variable x does not equal zero at step 930, the microprocessor360 determines that the rising edge that was just received at step 910is a data edge of a data pattern. The microprocessor 360 sets a measuredoffset time T_(M-OS) equal to rising edge time t_(E) minus the referenceedge time T_(REF-E) at step 936, i.e.,

T _(M-OS) =t _(E) −t _(REF-E).

The microprocessor 360 then executes a receive data procedure 1000 todetermine the bits of data that are encoded in the measured offset timeT_(M-OS) calculated at step 938, and the receiving procedure 900 exits.

FIG. 15 is a simplified flowchart of the receive data procedure 1000executed by the microprocessor 360 to determine the bits of data thatare encoded in the measured offset time period T_(M-OS) from thereceiving procedure 900. The microprocessor 360 uses a variable y tokeep track of which bits of the digital message are presently beingreceived, where a value of one for the variable y represents the firstbit and a value equal to the total number N_(DM) of bits of the digitalmessage represents the last bit of the digital message. Themicroprocessor 360 first determines if the measured offset time periodT_(M-OS) is equal to one of the offset time periods T_(OS1), T_(OS2),T_(OS3), T_(OS4) within the default tolerance ΔT_(OS). Specifically, ifthe measured offset time period T_(M-OS) is approximately equal to thefirst offset time T_(OS1) at step 1010, i.e.,

if (T _(OS1) −ΔT _(OS))<T _(M-OS)≦(T _(OS1) +ΔT _(OS)),

the microprocessor 360 sets the next two bits of the digital message inthe RX buffer RX[y+1,y] equal to “00” at step 1012. Similarly, if themeasured offset time period T_(M-OS) is approximately equal to thesecond offset time period T_(OS2) at step 1014, the third offset timeperiod T_(OS3) at step 1018, or the fourth offset time period T_(OS4) atstep 1022, the microprocessor 360 sets the next two bits of the digitalmessage in the RX buffer RX[y+1,y] equal to “01” at step 1016, to “10”at step 1020, or to “11” at step 1024, respectively.

If the variable y is not equal to the total number N_(DM) of bits of thedigital message minus one at step 1026, the microprocessor 360 increasesthe variable y by two at step 1028 and the receive data procedure 1000exits. If the variable y is equal to the total number N_(DM) of bits ofthe digital message minus one at step 1026 (i.e., the digital messagepresently being received is complete), the microprocessor 360 sets thevariable y to one at step 1030 and sets a message-received (MSG-RX) flagat step 1032, such that the microprocessor will process the receiveddigital message after the receive data procedure 1000 exits. Inaddition, the microprocessor 360 will begin to once again continuallymonitor the control-hot voltage V_(CH) to determine if the digitalballast controller has transmitted a start symbol.

FIG. 16 is an alternative example timing diagram of a control-hotvoltage V_(CH) generated by a digital ballast controller (e.g., thedigital ballast controller 120 of the load control system 100 shown inFIG. 1). As shown in FIG. 16, each data pattern has a half-cycle havinga reference edge and a number N_(DP) of subsequent half-cycles havingdata edges. For example, there may be two data edges per reference edgeas shown in FIG. 16. The digital ballast controller 120 is operable togenerate a reference edge during a first half-cycle and then to generatedata edges in each of the next two half-cycles. Accordingly, the digitalballast controller 120 is operable to transmit four bits of data everythree half-cycles (i.e., every 1.5 line cycles). The value of the datarepresented by the data edge in the second half-cycle is dependent uponthe offset time T_(OS) between the data edge and the reference edge inthe first half-cycle. The value of the data represented by the data edgein the third half-cycle is dependent upon the offset time T_(OS) betweenthe data edge in the third half-cycle and the time in the secondhalf-cycle that is the first offset time period T_(OS1) from thereference edge in the first half-cycle. In other words, the value of thedata represented by the data edge in the third half-cycle is dependentupon the offset time period T_(OS) between the data edge in the thirdhalf-cycle and the reference edge in the first half-cycle minus thefirst offset time period T_(OS1).

FIG. 17 is an alternative example timing diagram of a control-hotvoltage V_(CH) showing a start pattern used to start a digital messagetransmitted by a digital ballast controller (e.g., the digital ballastcontroller 120 of the load control system 100 shown in FIG. 1). Thedigital ballast controller 120 is operable to transmit the start patternby generating a reference edge during a first half-cycle, rendering thecontrollably conductive device 210 conductive in a second subsequenthalf-cycle at the first offset period T_(OS1) from the reference edge inthe first half-cycle (i.e., transmitting bits “00”), and then renderingthe controllably conductive device conductive after the start symboltime period T_(START) after the firing time in the previous half-cycle.The start symbol time period T_(START) is unique from and longer thanthe offset time periods T_(OS1)-T_(OS4) used to transmit data to thedigital dimming ballasts 110 (i.e., approximately 8.73 milliseconds).After transmitting the start pattern, the digital ballast controller 120is operable to immediately begin transmitting data in the next linecycle by generating a reference edge in the next half-cycle and dataedges in the subsequent half-cycles as shown in FIG. 17.

FIG. 18 is an example flowchart of a timer interrupt procedure 1100 thatis executed by a control circuit of a digital ballast controller (e.g.,the microprocessor 214 of the digital ballast controller 120, 200) totransmit a digital message having two data edges for each reference edge(e.g., as shown in FIG. 16). The timer interrupt procedure 1100 isexecuted by the microprocessor 214 when the value of the timer equalsthe set interrupt time, and is very similar to the timer interruptprocedure 700 shown in FIG. 12. However, when the variable m is notequal to zero at step 714 and is not equal to the number N_(DP) of dataedges in each data pattern (e.g., two) at step 1110, the microprocessor214 sets the base time t₀ equal to the base time t₀ from the previoushalf-cycle plus the first offset time period T_(OS1) at step 1112,before increasing the variable m by one at step 1114 and executing adata edge procedure (e.g., the data edge procedure 800 shown in FIG.13). During the data edge procedure 800, the microprocessor 214 sets theinterrupt time of the next timer interrupt equal to the base time t₀plus the first offset time period T_(OS1) at step 816 if themicroprocessor 214 is presently transmitting the first bit of the startpattern, and sets a timer interrupt for the interrupt time of the nexttimer interrupt equal to the base time t₀ plus the start symbol timeperiod T_(START) at step 816 if the microprocessor 214 is presentlytransmitting the last bit of the start pattern. Referring back to FIG.18, if the variable m is not equal to zero at step 714, but is equal tothe number N_(DP) of data edges in each data pattern at step 1110, themicroprocessor 214 sets the variable m to zero at step 720 and the timerinterrupt procedure 1100 exits.

FIG. 19 is an example flowchart of a receiving procedure 1200 executedby a control circuit of a digital dimming ballast (e.g., themicroprocessor 360 of one of the digital dimming ballasts 110 of theload control system 100 shown in FIG. 1) to receive a digital messagehaving two data edges for each reference edge (e.g., as shown in FIG.16). The microprocessor 360 executes the receiving procedure 1200periodically (e.g., once every half-cycle) to receive the digitalmessages from a digital ballast controller (e.g., the digital ballastcontroller 120 shown in FIG. 1). The receiving procedure 1200 is verysimilar to the receiving procedure 900 shown in FIG. 14. However, in thereceiving procedure 1200 shown in FIG. 19, the microprocessor 360determines that a start pattern has been received by determining thatthe time periods T₁, T₂ between the rising edges in two consecutivehalf-cycles are equal to the first offset time period T_(OS1) and thestart symbol time period T_(START). Specifically, the microprocessor 360sets the first time period T₁ equal to the previous second time periodT₂ and sets the second time period T₂ equal to the rising edge timet_(E) minus a previous rising edge time t_(E-PREV) at step 1210, anddetermines that a start pattern has been received if the first period T₁is equal to the first offset time period T_(OS1) within the defaulttolerance ΔT_(OS) at step 1212 and the second period T₂ is equal to thestart symbol time period T_(START) within the default tolerance ΔT_(OS)at step 1214.

In addition, the microprocessor 360 calculates the measured offset timeT_(M-OS) in dependence upon the variable x at step 1216, i.e.,

T _(M-OS)=(t _(E) −t _(REF-E))−(x−1)*T _(OS1),

before executing the receive data procedure 1000 to determine the bitsof data that are encoded in the measured offset time T_(M-OS). If thevariable x is not equal to the number N_(DP) of data edges in each datapattern at step 1218, the microprocessor 360 increments the variable xby one at step 1220 and the receiving procedure 1200 exits. If thevariable x is equal to the number N_(DP) of data edges in each datapattern at step 1218, the microprocessor 360 sets the variable x to zeroat step 1222 and the receiving procedure 1200 exits.

Alternatively, the digital ballast controller 120 could transmit and thedigital ballasts 110 could receive more than two data edges perreference edge using the timer interrupt procedure 1100 of FIG. 18 andthe receiving procedure 1200 of FIG. 19 if the number N_(DP) of dataedges in each data pattern is greater than two.

As previously mentioned, in some retrofit applications, the neutral wirecoupled to the neutral side of the AC power source 102 may not beavailable in the wallbox of the digital ballast controllers 120. FIG. 20is a simplified block diagram of a load control system 1300 comprising atwo-wire remote control device, e.g., a two-wire digital ballastcontroller 1320 that does not require a connection to the neutral sideof an AC power source. The digital ballast controller 1320 is adapted tobe coupled in series electrical connection between an AC power source1302 and two-wire digital dimming ballasts 1310 (which may be the sameas the digital dimming ballasts 110, 300 shown in FIGS. 1 and 3B)without a connection to the neutral side of the AC power source. Thedigital ballast controller 1320 is operable to transmit digital messagesto the digital dimming ballast 1310 in response to RF signals 1306transmitted by wireless control devices, e.g., a wireless occupancysensor 1330, a wireless daylight sensor 1340, and a battery-poweredremote control 1350 (which may be the same as the wireless occupancysensor 130, the wireless daylight sensor 140, and the battery-poweredremote control 150 of the load control system 100 shown in FIG. 1).

The load control system 1300 further comprises an active load circuit1390 that is coupled in parallel with the two-wire digital dimmingballasts 1310 for providing a path for a charging current of a powersupply 1420 (FIG. 21) of the digital ballast controller 1320 to beconducted as will be described in greater detail below. For example, theactive load circuit 1390 may be housed in an enclosure and wired to thecircuit wiring in one of the lighting fixtures with one of the ballasts1310 of the load control system 1300. In addition, the active loadcircuit 1390 could be included as part of a retrofit kit (e.g., theretrofit kit 180 shown in FIG. 5). Alternatively, the active loadcircuit 1390 could be included in each of the ballasts 1310 of the loadcontrol system 1300, e.g., coupled between the control-hot terminal CHand the neutral terminal N.

FIG. 21 is a simplified block diagram of a digital ballast controller1400 and an active load circuit 1490 (e.g., the digital ballastcontroller 1320 and the active load circuit 1390, respectively, of theload control system 1300 of FIG. 20). The digital ballast controller1400 is able to transmit digital messages to the digital dimmingballasts using any of the communication techniques discussed above withreference to FIGS. 1-19. The digital ballast controller 1400 furthercomprise a zero-crossing detector 1416 that is coupled in parallel witha controllably conductive device 1410 for determining the zero-crossingsof the AC power source 1302. In addition, the power supply 1420 is alsocoupled in parallel with the controllably conductive device 1410 and isoperable to conduct a charging current I_(CHRG) to generate a DC supplyvoltage V_(CC) for powering a microprocessor 1414, a memory 1418, andother low-voltage circuitry of the digital ballast controller 1400. Thepower supply 1420 is operable to charge when the controllably conductivedevice 1410 is non-conductive at the beginning of each half-cycle of anAC power source 1402.

When the controllably conductive device 1410 is non-conductive, thepower supply 1420 is coupled in series with the ballasts 1310 across theAC power source 1402, such that the AC source voltage of the AC powersource 1402 is split between the power supply and the ballasts, and themagnitude of the control-hot voltage V_(CH) across the ballasts dependsupon the relative impedance of the ballasts and the power supply. It isimportant to keep the magnitude of the control-hot voltage V_(CH) acrossthe ballasts 1310 well below the rising threshold V_(TH-R) of an edgedetect circuit (e.g., the edge detect circuit 380) of the ballastsduring the time that the controllably conductive device 1410 isnon-conductive. To meet this need, the impedance between the control-hotterminal CH of the digital ballast controller 1320 and the neutral sideof the AC power source 1402 (i.e., across the ballasts 1310) must belower than the impedance between the hot terminal H and the control-hotterminal CH of the digital ballast controller 1320 during the time thatthe controllably conductive device 1410 is non-conductive. Accordingly,the two-wire digital ballast controller 1320 shown in FIG. 21 comprisesa current limit circuit 1430 in series electrical connection with thepower supply 1420 to limit the magnitude of the charging currentI_(CHRG) to be equal to or less than a first current limit L_(LIMIT1).The value of the first current limit I_(LIMIT1) depends on the currentrequirements of the power supply 1420 and is chosen so that the powersupply can fully recharge during the time that the controllablyconductive device 1410 is non-conductive each half-cycle.

The active load circuit 1490 conducts an active load current I_(AL)having a magnitude that is approximately equal to the magnitude of thecharging current I_(GHRG) of the power supply 1420 of the digitalballast controller 1320 when the controllably conductive device 1410 isnon-conductive each half-cycle. The active load circuit 1490 comprises acurrent limit circuit 1492 that operates to ensure that the magnitude ofthe active load current I_(AL) is maintained equal to or less than asecond current limit I_(LIMIT2), which is selected to be greater thanthe first current limit L_(LIMIT1) of the digital ballast controller1320. For example, the magnitude of the second current limit I_(LIMIT2)may be approximately 1.2 times greater than the magnitude of the firstcurrent limit I_(LIMIT1). As long as the magnitude of the first currentlimit I_(LIMIT1) is lower than the magnitude of the second current limitI_(LIMIT2), the magnitude of the control-hot voltage V_(CH) across theballasts 1310 (i.e., across the active load circuit 1490) will beapproximately zero volts during the time that the controllablyconductive device 1410 is non-conductive each half-cycle.

When the controllably conductive device 1410 becomes conductive, thecurrent available will be much greater than second current limitI_(LIMIT2), so the magnitude of the control-hot voltage V_(CH) acrossthe ballasts 1310 will be able to increase up towards the magnitude ofthe AC source voltage of the AC power source 1402. To preventunnecessary power dissipation, the active load circuit 1490 comprises avoltage threshold circuit 1494 that is coupled in parallel with thecurrent limit circuit 1492 and operates to disable the current limitcircuit when the magnitude of the control-hot voltage V_(CH) across theactive load circuit 1490 exceeds an active-load-disable thresholdV_(TH-ALD) (e.g., approximately 30 volts). The voltage threshold circuit1494 has a time delay that requires the magnitude of the control-hotvoltage V_(CH) across the active load circuit 1490 to be below theactive-load-disable threshold V_(TH-ALD) for a period of time, e.g.approximately 400 microseconds, before re-enabling the current limitcircuit 1492. This time delay significantly reduces the amount ofcurrent drawn by the active load circuit 1490 near the end of each linehalf-cycle as the magnitude of the control-hot voltage V_(CH) approacheszero volts.

FIG. 22 is a simplified block diagram of a lighting control system 1500comprising a digital dimming ballast 1510 that is directly connected toone or more input devices, such as an occupancy sensor 1530 and adaylight sensor 1540. The occupancy sensor 1530 and the daylight sensor1540 may be mounted to the lighting fixture in which the digital dimmingballast 1510 is installed, and may be included as part of a retrofit kitincluding the digital dimming ballast 1510. The digital dimming ballast1510 is adapted to operate as a “mini-system” to control the intensityof a connected lamp 1504 in response to the occupancy sensor 1530 andthe daylight sensor 1540. Dimming ballasts adapted to be directlyconnected to one or more input devices, such as sensors, are describedin greater detail in previously-referenced U.S. Pat. No. 7,619,539.

The digital dimming ballast 1510 is also operable to control theintensity of the connected lamp 1504 in response to “broadcast” commandstransmitted by the digital ballast controller 1520 via the control-hotvoltage V_(CH). The digital ballast controller 1520 is operable totransmit the broadcast commands to the digital dimming ballast 1510 inresponse to RF signals 106 transmitted by a broadcast controller 1560(i.e., a central controller) of the load control system 1500. Thebroadcast controller 1560 is connected to a network 1562 (e.g., a localarea network or the Internet) via a network communication link 1564(e.g., an Ethernet link) for receiving the broadcast commands totransmit to the digital dimming ballast 1510. The broadcast commands maycomprise, for example, at least one of a timeclock command, a load shedcommand, or a demand response command. The digital ballast controller1520 is operable to transmit information, such as the status and energyconsumption of the controlled loads, back to the broadcast controller1560, which may share the information with other control devices coupledon the network 1562. The broadcast controller 1560 is described ingreater detail in commonly-assigned U.S. patent application Ser. No.13/725,105 filed Dec. 21, 2012, entitled LOAD CONTROL SYSTEM HAVINGINDEPENDENTLY-CONTROLLED UNITS RESPONSIVE TO A BROADCAST CONTROLLER, theentire disclosure of which is hereby incorporated by reference.

The digital ballast controller 1520 is also operable to transmit digitalmessages to the digital dimming ballast 1510 in response to RF signals1506 transmitted by wireless control devices, e.g., a wireless occupancysensor 1530, a wireless daylight sensor 1540, and a battery-poweredremote control 1550 (which may be the same as the wireless occupancysensor 130, the wireless daylight sensor 140, and the battery-poweredremote control 150 of the load control system 100 shown in FIG. 1). Inaddition, the digital ballast controller 1520 may be directly connectedto one or more input devices, such as the occupancy sensor 1530 and thedaylight sensor 1540.

FIG. 23 is a simple wiring diagram of a load control system 1600 havinga digital LED controller 1620 and a plurality of two-wire LED drivers1610 for controlling the intensity of respective LED light sources 1604(i.e., LED light engines). The digital LED controller 1620 may beidentical to the digital ballast controller 120, 200 shown in FIGS. 1and 3A, and may be able to transmit digital messages to the LED drivers1610 using the communication techniques described above. For example,the digital LED controller 1620 may transmit digital messages includingcommands to turn the LED light sources 1604 on and off, to control theintensity of each of the LED light sources, and to adjust the colortemperature (i.e., the color) of each of the LED light sources. Inaddition, the digital LED controller 1620 may have a connection to theneutral side of an AC power source 1602 as shown in FIG. 22 or mayalternatively be a two-wire device (e.g., the digital ballast controller1320 shown in FIG. 21). The digital LED controller 1620 is also operableto transmit digital messages to the LED drivers 1610 in response to RFsignals 1606 transmitted by wireless control devices, e.g., a wirelessoccupancy sensor 1630, a wireless daylight sensor 1640, and abattery-powered remote control 1650 (which may be the same as thewireless occupancy sensor 130, the wireless daylight sensor 140, and thebattery-powered remote control 150 of the load control system 100 shownin FIG. 1). Examples of LED drivers are described in greater detail inco-pending, commonly-assigned U.S. patent application Ser. No.12/813,908, filed Jun. 11, 2010, entitled LOAD CONTROL DEVICE FOR ALIGHT-EMITTING DIODE LIGHT SOURCE, the entire disclosure of which ishereby incorporated by reference. Alternatively, both digital dimmingballasts 110, 300 and LED drivers 1610 could be coupled to a singledigital ballast controller 120, 200, 1620, such that the digital ballastcontroller is able to control multiple load types in a single loadcontrol system.

The digital ballast controllers 120, 200, 1320, 1400 and LED controllers1620 as described herein generate the control-hot voltage V_(CH) suchthat the control-hot voltage resembles a forward phase-control voltage,i.e., the controllably conductive device of the digital ballastcontroller is rendered conductive at a firing time each half-cycle andthe data is encoded in time periods between the timing edges (i.e.,rising edges) of the control-hot voltage. Alternatively, the digitalballast controllers 120, 200, 1320, 1400 and LED controllers 1620 couldrender the controllably conductive device non-conductive at some timeeach half-cycle, such that the control-hot voltage V_(CH) resembles areverse phase-control voltage and the data is encoded in time periodsbetween the timing edges (i.e., falling edges) of the control-hotvoltage. In addition, the control-hot voltage V_(CH) could comprise acenter phase-control voltage having both a rising edge towards thebeginning of a half-cycle and a falling edge towards the end of thehalf-cycle. When the control-hot voltage V_(CH) is a reversephase-control voltage or a center phase-control voltage, thecontrollably conductive device may be implemented as, for example, twoFETs in anti-series connection.

FIG. 24 is a simple wiring diagram of a two-way load control system 1700having a plurality of two-wire power devices that may comprise, forexample, two-wire load control devices, such as two-wire digital dimmingballasts 1710 for controlling respective fluorescent lamps 1704, andtwo-wire input devices, such as a two-wire line-voltage occupancy sensor1770. In addition, the power devices of the load control system 1700 maycomprise additional types of two-wire load control devices, such as, forexample, light-emitting diode (LED) drivers for driving LED lightsources; screw-in luminaries having integral light sources and loadcontrol circuits; dimming circuits for controlling the intensity oflighting loads; interface devices (e.g., a device that is operable toreceive a control-hot voltage signal V_(CH) and accordingly control apower device for example, by providing a 0-10V signal), electronicswitches, controllable circuit breakers, or other switching devices forturning electrical loads or appliances on and off; plug-in load controldevices, controllable electrical receptacles, or controllable powerstrips for controlling plug-in electrical loads (such as coffee pots andspace heaters); motor control units for controlling motor loads, such asceiling fans or exhaust fans; drive units for controlling motorizedwindow treatments or projection screens; motorized interior or exteriorshutters; thermostats for heating and/or cooling systems; temperaturecontrol devices for controlling heating, ventilation, and airconditioning systems; air conditioners; compressors; electric baseboardheater controllers; controllable dampers; humidity control units;dehumidifiers; water heaters; pool pumps; refrigerators; freezers;televisions or computer monitors; power supplies; audio systems andamplifiers; generators; electric chargers, such as electric vehiclechargers; and alternative energy controllers (e.g., solar, wind, orthermal energy controllers). Further, the power devices of the loadcontrol system 1700 may comprise additional types of two-wire inputdevices, such as, for example, a vacancy sensor, a daylight sensor, atemperature sensor, a humidity sensor, a pressure sensor, a securitysensor, a proximity sensor, a smoke detector, a carbon monoxidedetector, a wall-mounted keypad, a remote control keypad, a key fob, acell phone, a smart phone, a tablet, a personal digital assistant (PDA),a personal computer, a timeclock, an audio-visual control, a safetydevice (such as a fire protection, water protection, medical emergencydevice), a power monitoring device (such as a power meter, an energymeter, a utility submeter, and a utility rate meter), one or morepartition switches, a central control transmitter, or any residential,commercial, or industrial controller.

A digital power device controller 1720 (i.e., a remote control device)is adapted to be coupled in series electrical connection between an ACpower source 1702 and the parallel combination of the power devices(i.e., the digital dimming ballasts 1710 and the line-voltage occupancysensor 1770) via a circuit wiring 1714. The digital power devicecontroller 1720 may be a wallbox device that is able to replace astandard mechanical switch. As shown in FIG. 24, the power devicecontroller 1720 does not require a connection to the neutral side of theAC power source 1702. The digital power device controller 1720 is ableto communicate with the digital dimming ballasts 1710 to cause thefluorescent lamps 1704 to turn on in response to an actuation of an onbutton 1722 and to cause the fluorescent lamps to turn off in responseto an actuation of an off button 1724. The digital power devicecontroller 1720 is also able to cause the digital dimming ballasts 1710to raise the intensity of the fluorescent lamps 1704 (e.g., by anincrement) in response to an actuation of a raise button 1726 and tocause the digital dimming ballasts to lower the intensity of thefluorescent lamps in response to an actuation of a lower button 1728.Alternatively, the digital ballast controller 1720 may comprisedifferent user interfaces and form factors as shown in FIG. 2B.

The digital power device controller 1720 may be configured to cause thedigital dimming ballasts 1710 to control the intensities of thefluorescent lamps 1704 to a predetermined intensity level (e.g., apreset, an emergency level, etc). The digital power device controller1720 may be configured to cause the digital dimming ballasts 1710 to“fade” the intensities of the fluorescent lamps 1704 (e.g., slowlyadjust the intensities over a predetermined period of time or at apredetermined fade rate). For example, the digital dimming ballasts 1710may be configured to fade the intensities of the fluorescent lamps 1704over a predetermined number of half-cycles, and may keep track of thefade time in terms of a number of half-cycles.

The power devices of FIG. 24 are operable to both transmit and receivedigital messages with the digital power device controller 1720 viaphase-control voltages on the circuit wiring 1714 (e.g., providingtwo-way communication) as will be described in greater detail below. Thedigital power device controller 1720 is also responsive to digitalmessages received via RF signals 1706 from wireless input devices, e.g.,an occupancy sensor 1730, a daylight sensor 1740, and a battery-poweredremote control 1750, which may operate in a similar manner as theoccupancy sensor 130, the daylight sensor 140, and the battery-poweredremote control 150 shown in FIG. 1. The digital power device controller1720 may also be directly connected to one or more input devices (suchas the occupancy sensor 1530 and the daylight sensor 1540 shown in FIG.22). In addition, the digital power controller 1720 may be operable totransmit RF signals 1706 to other digital power device controllers. Theload control system 1700 is able to provide all of the advantages of aload control system having a two-way digital communication link withoutrequiring any additional wiring. This means that the load control system1700 appears the same as the prior art digital load control systemsduring programming and normal operation, but is vastly easier toinstall.

The digital power device controller 1720 generates a control-hot voltageV_(CH) (i.e., a phase-control voltage), which is coupled across and isreceived by the power devices. A controller-drop voltage V_(CD) isgenerated across the digital power device controller 1720 and is thedifference between the AC mains line voltage and the control-hot voltageV_(CH). The digital power device controller 1720 is operable to transmita “forward” digital message to the power devices by encoding digitalinformation in the firing times of the timing edges of the control-hotvoltage V_(CH) as described above with reference to FIGS. 1-23. To allowfor two-way communication, the power devices are operable to transmit a“reverse” digital message to the digital power device controller 1720 byencoding digital information in the controller-drop voltage V_(CD)developed across the digital power device controller as will bedescribed in greater detail below. Particularly, the power devices areoperable to transmit a reverse digital message to the digital powerdevice controller 1720 in response to receiving a forward digitalmessage from the digital power device controller. In addition, the powerdevices are operable to transmit acknowledgements to the digital powerdevice controller 1720 after receiving a forward digital message, suchthat the digital power device controller is operable to determine if allof the power devices have successfully received the digital message. Asused herein, “forward” communication refers to digital messagestransmitted from the digital power device controller 1720 and “reverse”communication refers to digital messages transmitted from the powerdevices (e.g., the two-wire digital dimming ballasts 1710 and thetwo-wire line-voltage occupancy sensor 1770). Forward communication isvery similar to the communication technique as described above inregards to FIGS. 1-23.

Each power device may have a serial number (e.g., a 24-bit uniquenumber) stored in memory, for example, during the manufacturing processof the power device. During a commissioning procedure of the two-wayload control system 1700, the digital power device controller 1720 maybe put into an addressing mode (e.g., in response to the actuation ofone or more of the on button 1722, the off button 1724, the raise button1726, and the lower button 1728). In the addressing mode, the digitalpower device controller 1720 is operable to assign a unique identifier(e.g., a link or short address) to each of the power devices coupled tothe digital power device controller. The link address may be smallerthan the serial number (e.g., 6 bits), such that there may be up to 64power devices coupled to the digital power device controller 1720. Thedigital power device controller 1720 may use the link addresses totransmit forward digital messages directly to specific power devices. Inaddition, the digital power device controller 1720 may be operable totransmit broadcast messages to all of the power devices (e.g., thedigital dimming ballasts 1710 and the line-voltage occupancy sensor1770) or to a subset (e.g., a group) of the power devices.

Since the power devices are each assigned a link address during theaddressing mode, the power devices do not require DIP switches, rotaryencoders, jumpers, or other hardware means for setting the address (orcontrol channel). Therefore, because the digital dimming ballasts 1710of FIG. 24 does not have DIP switches (or other structures) that need tobe physically adjusted during installation of the ballast, the ballastmay be installed just like a prior art non-dim ballast (particularlywhen the ballast is included in a retrofit kit having dimmable lampsockets). Accordingly, the load control system 1700 can be configuredduring the commissioning procedure without accessing (i.e., makingphysical contact with) the power devices (or the electrical loadscontrolled by the load control devices), which may be remotely locatedand not easily accessible. In addition, the load control system 1700 canbe re-configured after commissioning to provide for differentfunctionality of the system without accessing the power devices or theelectrical loads.

Because the power devices are each assigned a link address, the digitalpower device controller 1720 is operable to assign the power devices toone or more zones (i.e., groups) and then transmit forward digitalmessages to control only the power devices of one of the zones. Forexample, the digital power device controller 1720 could assign all ofthe digital dimming ballasts 1710 to the same zone, such that all of thedigital dimming ballasts 1710 will be responsive to the occupancysensors 1730, 1770 and the remote control 1750. Alternatively, some ofthe digital dimming ballast 1710 could be assigned to a first zone,which is responsive to the daylight sensor 1740, while the other digitaldimming ballasts could be assigned to a second zone, which is notresponsive to the daylight sensor. Methods of assigning digital dimmingballasts to groups are described in greater detail in commonly-assignedU.S. Patent Application Publication No. 2004/0217718, published Nov. 4,2004, entitled DIGITAL ADDRESSABLE ELECTRONIC BALLAST AND CONTROL UNIT,and U.S. Pat. No. 7,391,297, issued Jun. 24, 2008, entitled HANDHELDPROGRAMMER FOR LIGHTING CONTROL SYSTEM, the entire disclosures of whichare hereby incorporated by reference. Prior to being assigned a linkaddress, each power device could be operable to work out-of-box as asingle group. Specifically, the power devices could be operable torespond to a predetermined default group, for example, to be responsiveto the occupancy sensors 1730, 1770 and the remote control 1750, but notto the daylight sensor 1740.

During the commissioning procedure, the digital power device controller1720 may be put into a grouping mode (e.g., in response to the actuationof one or more of the on button 1722, the off button 1724, the raisebutton 1726, and the lower button 1728). The user may then actuate anactuator on one of the input devices (e.g., one of the occupancy sensors1730, 1770, the daylight sensor 1740, and the remote control 1750) tocreate a zone that is responsive to that input device. The digital powerdevice controller 1720 may then cause one of the digital dimmingballasts 1710 to flash the respective lamp 1704. The user may actuateactuators on the input device to assign the digital dimming ballast 1710of the flashing lamp to the zone or to cause another digital dimmingballast to flash the respective lamp. The user may step through eachdigital dimming ballast 1710 and assign the appropriate ballasts to thezone until all desired lamps 1704 are assigned to the zone.

Because the power devices are able to transmit the reverse digitalmessages in response to receiving forward digital messages, the digitalpower device controller 1720 can receive feedback information from thepower devices. For example, each digital dimming ballasts 1710 couldtransmit information regarding lamp status information (such asindications of missing or failed lamps) to the digital power devicecontroller 1720 in response to a forward digital message having a queryfor lamp status information. Methods of determining if a fluorescentlamp is missing or failed are described in greater detail incommonly-assigned U.S. Patent Application Publication No. 2006/0244395,published Nov. 2, 2006, entitled ELECTRONIC BALLAST HAVING MISSING LAMPDETECTION, and U.S. Patent Application Publication No. 2012/0043900,published Feb. 23, 2012, entitled METHOD AND APPARATUS FOR MEASURINGOPERATING CHARACTERISTICS IN A LOAD CONTROL DEVICE, the entiredisclosures of which are hereby incorporated by reference.

In addition, the line-voltage occupancy sensor 1770 may be operable totransmit information regarding occupancy and vacancy conditions detectedby the occupancy sensor in response to a forward digital message havinga query for such information. The digital power device controller 1720may be operable to transmit the feedback information received from thedigital dimming ballasts 1710 and the line-voltage occupancy sensor 1770to an external device, such as the broadcast controller 1560 shown inFIG. 22, which may share the information with other control devicescoupled on the network 1562.

As previously mentioned, the power devices may be two-wire load controldevices and two-wire input devices. The two-wire load control devicesare operable to control respective electrical loads in response to theforward digital messages received from the digital power devicecontrollers 1720. For example, the digital dimming ballasts 1710 areoperable to adjust the intensities of the lamps 1704 in response to theforward digital messages received from the digital power devicecontroller 1720. The digital power device controller 1720 is operable totransmit forward digital messages to all of the power devices (e.g., abroadcast message), to a subset (e.g., a group) of the power devices(e.g., the two-wire load control devices), or to individual powerdevices.

Each two-wire input device is operable to transmit a reverse digitalmessage to the digital power device controller 1720 and the other powerdevices in response to received inputs. The two-wire input devices maybe operable to transmit each reverse digital message in response toreceiving a forward digital message from the digital power devicecontroller 1720 (e.g., a query message). For example, the two-wireline-voltage occupancy sensor 1770 may be operable to transmit a reversedigital message including occupancy or vacancy information to thedigital power device controller 1720 in response to detecting anoccupancy or vacancy condition in the space and receiving a querymessage from the digital power device controller. The digital powerdevice controller 1720 may then transmit a forward digital message tothe digital dimming ballast 1710 to thus control the intensities of thelamps 1704 in response to the occupancy or vacancy information receivedfrom the line-voltage occupancy sensor 1770. Alternatively, each digitaldimming ballast 1710 may be operable to receive the reverse digitalmessage including the occupancy and vacancy information directly fromthe line-voltage occupancy sensor 1770 and to automatically control theintensity of the respective lamp 1704 in response to the occupancy andvacancy information. The two-wire input devices may be operable totransmit reverse digital messages directly to one or more of the otherpower devices. Since the two-wire load control devices and the two-wireinput devices are all coupled to the circuit wiring 1714, these powerdevices may easily be installed in the same location. For example, thetwo-wire line-voltage occupancy sensor 1770 may easily be integratedinto the lighting fixture in which one of the digital dimming ballasts1710 is installed. In addition, a retrofit kit including one of thetwo-wire digital dimming ballasts 1710 may also include the two-wireline-voltage occupancy sensor 1770.

Alternatively, the ballasts 1710 could comprise digital switchingballasts that are responsive to the digital messages transmitted by thedigital ballast controller 1720, but only to commands to turn therespective lamps on and off. In addition, the ballasts 1710 could alsoalternatively comprise digital bi-level switching ballasts that are ableto individually control (e.g., turn off and on) a plurality of lamps(e.g., two or three lamps per ballast) to provide a few discrete dimmedlevels (e.g., as described above with reference to FIG. 1). Further, theballasts 1710 could alternatively comprise emergency ballasts. Inaddition, the load control system 1700 could comprise two-wire digitalLED drivers for controlling respective LED light sources rather than thedigital dimming ballasts 1710.

The load control system 1700 may comprise multiple types of two-wireload control devices coupled to a single digital power device controller1720. For example, the power devices coupled to the digital power devicecontroller 1720 may comprise at least one two-wire digital dimmingballast and as least one two-wire digital LED driver.

Because the power devices are operable to transmit acknowledgements tothe digital power device controller 1720, the digital power devicecontroller is operable to transmit new values of operating settings tothe power devices and receive confirmation that the new values werereceived by the power devices. For example, the digital power devicecontroller 1720 may be operable to transmit new values for the low-endintensity L_(LE), the high-end intensity L_(HE), a ballast factor, or ademand response setting to the digital dimming ballasts 1710. Also thedigital power device controller 1720 may be operable to transmit newvalues of operating settings (such as timeout period, sensitivity, etc)to the occupancy sensor 1770. The digital power device controller 1720may maintain a record in memory of the present operational settings ofthe power devices. The digital power device controller 1720 may also beoperable to download new firmware to the power devices. This allows theload control system to adapt to new types of power devices and to changethe functionality of the power devices after installation.

The digital power device controller 1720 is operable to automaticallyidentify power devices that are missing and new power devices that havebeen coupled to the digital power device controller. Since the digitalpower device controller 1720 is able to keep track of the presentoperational settings of the power devices in memory, the missing orfailed power devices may be easily replaced and reprogrammed in the loadcontrol system 1700. For example, if one of the digital dimming ballasts1710 has failed and a new ballast is installed, the digital power devicecontroller 1720 is able to determine which of the digital dimmingballasts is missing. The digital power device controller 1720 can thenassign the new ballast a link address and then transmit the operationalsettings of the failed ballast to the new ballast. Methods of replacingdigital dimming ballasts in a lighting control system are described ingreater detail in commonly-assigned U.S. Patent Application PublicationNo. 2009/0273433, published Nov. 5, 2009, entitled METHOD OFAUTOMATICALLY PROGRAMMING A NEW BALLAST ON A DIGITAL BALLASTCOMMUNICATION LINK; U.S. Patent Application Publication No.2010/0241255, published Sep. 23, 2010, entitled METHOD OF SEMI-AUTOMATICBALLAST REPLACEMENT; and U.S. Patent Application Publication No.20110115293, published May 19, 2011, entitled METHOD FOR REPLACING ALOAD CONTROL DEVICE OF A LOAD CONTROL SYSTEM; the entire disclosures ofwhich are hereby incorporated by reference.

The digital power device controller 1720 may also be configured toassign a circuit address to each of the power devices that are connectedto that digital power device controller 1720 via the circuit wiring1714. For example, the power devices on the circuit wiring 1714 may allsave the exact same circuit address in memory. The digital power devicecontroller 1720 may transmit the circuit address to each power device atthe same time that the digital power device controller transmits thelink address to the power device (during the commissioning procedure).The digital power device controller 1720 is configured to periodicallytransmit out broadcast messages including the circuit address. If apower device having a circuit address is ever disconnected from thecircuit wiring 1714 connected to the digital power device controller1720 and then connected to another different digital power devicecontroller, the power device will receive a broadcast message includinga different circuit address and will reset its circuit address, linkaddress, and other configuration information after receiving thebroadcast message including the different circuit address apredetermined number of times. The power device can then obtain acircuit address and a new link address from the different digital powerdevice controller.

FIG. 25 is a simplified block diagram of an example digital power devicecontroller 1820 (e.g., the digital power device controller 1720) that isable to transmit forward digital messages to and receive reverse digitalmessages from one or more power devices (e.g., the power devices of theload control system 1700 of FIG. 24). The digital power devicecontroller 1820 comprises a hot terminal H adapted to be coupled to theAC power source 1702 and a control-hot terminal CH adapted to be coupledto the power devices. The digital power device controller 1820 couldalternatively comprise a neutral terminal adapted to be coupled to theneutral side of the AC power source 1702 (as with the digital ballastcontroller 120 shown in FIG. 1).

The digital power device controller 1820 comprises a controllablyconductive device, e.g., a triac 1810 as shown in FIG. 25, adapted to becoupled in series electrical connection between the AC power source 1702and the power devices for generating a control-hot voltage V_(CH). Thetriac 1810 is operable to conduct a load current L_(LOAD) of all of thepower devices coupled to the digital power device controller 1820. Sincethe triac 1810 is coupled between the AC power source 1702 and the powerdevices, the control-hot voltage V_(CH) may only exist on the circuitwiring 1714 between the digital power device controller 1820 and thepower devices (i.e., the digital power device controller operates to“swallow” the forward and reverse digital messages). Accordingly, thecontrol-hot voltage V_(CH) does not interfere with other control devicesthat may be coupled to the AC power source 1702.

The digital power device controller 1820 further comprises amicroprocessor 1814 that generates a drive voltage V_(DR) for renderingthe triac 1810 conductive to thus generate the control-hot voltageV_(CH) at the control-hot terminal CH. The microprocessor 1814 mayalternatively comprise, for example, a microcontroller, a programmablelogic device (PLD), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or any suitable processing device,controller, or control circuit. The microprocessor 1814 receives inputsfrom a zero-crossing detector 1816 (which may be the same as thezero-crossing detector 216 of the digital ballast controller 200 shownin FIG. 3A) and one or more actuators 1818 (e.g., the on button 1722,the off button 1724, the raise button 1726, and the lower button 1728 ofthe digital power device controller 1720 shown in FIG. 24). Themicroprocessor 1814 may also be coupled to a wireless communicationcircuit, e.g., an RF transceiver 1822, which is coupled to an antenna1824 for transmitting and receiving the RF signals 1706. Alternatively,the wireless communication circuit may comprises an RF transmitter fortransmitting RF signals, an RF receiver for receiving RF signals, or aninfrared (IR) receiver for receiving IR signals. The microprocessor 1814may further be coupled to a visual display 1826 (which may comprise, forexample, the status indicators 128 of the digital ballast controller 120shown in FIG. 1). The microprocessor 1814 may also store operationalcharacteristics and information in a memory (not shown), which may be anexternal IC or an internal circuit of the microprocessor.

The digital power device controller 1820 comprises a full-wave rectifierbridge 1840 having AC terminals that are coupled in series with aresistor R1842 across the triac 1810. The digital power devicecontroller 1820 also includes a gate coupling circuit 1850 that iscoupled across the DC terminals of the rectifier bridge 1840. The gatecoupling circuit 1850 comprises a voltage-controlled controllablyconductive device, such as a MOS-gated transistor, e.g., a FET Q1852.The gate coupling circuit 1850 receives the drive voltage V_(DR) fromthe microprocessor 1814 for rendering the FET Q1852 conductive andnon-conductive. Specifically, the drive voltage V_(DR) is coupled to agate of the FET Q1852 through a FET drive circuit 1854 and a gateresistor R1855. The gate coupling circuit 1850 also comprises a currentlimit circuit including an NPN bipolar junction transistor Q1856 and asense resistor R1858, which is coupled in series with the FET Q1852. Thebase of the transistor Q1856 is coupled to the junction of the FET Q1852and the sense resistor R1858. Accordingly, in the event of anovercurrent condition (i.e., when the magnitude of the voltage acrossthe sense resistor R1858 exceeds the rated base-emitter voltage of thetransistor Q1856), the transistor Q1856 is rendered conductive, thuspulling the gate of the FET Q1852 down towards circuit common andrendering the FET non-conductive.

The digital power device controller 1820 also comprises a controllableswitching circuit 1860 coupled between the gate of the triac 1810 andthe junction of the rectifier bridge 1840 and the resistor 1842.Accordingly, the controllable switching circuit 1860 is operativelycoupled in series between the gate coupling circuit 1850 and the gate ofthe triac 1810. The microprocessor 1814 generates a switch controlvoltage V_(SW) for rendering the controllable switching circuit 1860conductive and non-conductive. When the controllable switching circuit1860 is conductive, the FET Q1852 of the gate coupling circuit 1850 isable to conduct a gate current I_(G) through the gate of the triac 1810to render the triac conductive to generate the control-hot voltageV_(CH).

The digital power device controller 1820 also includes a power supply1821 that is coupled in series with a current-limit circuit 1830 acrossthe DC terminals of the rectifier bridge 1840. The power supply 1821 isoperable to generate a first DC supply voltage V_(CC1) for driving theFET Q1852 of the gate coupling circuit 1850 and a second DC supplyvoltage V_(CC2) for powering the microprocessor 1814 and otherlow-voltage circuitry of the digital power device controller. The powersupply 1821 is operable to charge by conducting a charging currentI_(CHRG) through the control-hot terminal CH when the triac 1810 isnon-conductive at the beginning of each half-cycle of the AC powersource 1702. The current limit circuit 1830 limits the magnitude of thecharging current I_(CHRG) to be equal to or less than a first currentlimit I_(LIMIT1), e.g., approximately 150 milliamps. The microprocessor1814 generates a current-limit control signal V_(CL) that is coupled tothe current-limit circuit 1830, such that the microprocessor is able torender the current-limit circuit 1830 non-conductive to stop the powersupply 1821 from charging as will be described in greater detail below.

The digital power device controller 1820 also comprises a reversecommunication receiving circuit 1870 that is coupled across the DCterminals of the rectifier bridge 1840, such that the reversecommunication receiving circuit 1870 is responsive to thecontroller-drop voltage V_(CD) developed across the digital power devicecontroller. The reverse communication receiving circuit 1870 provides areverse communication receive signal V_(R-RX) to the microprocessor1814, such that the microprocessor is able to decode the digitalinformation encoded in the controller-drop voltage V_(CD) by the powerdevices as will be described in greater detail below.

FIG. 26 is a simplified block diagram of an example digital dimmingballast 1910 (e.g., one of the digital dimming ballasts 1710) that isable to receive forward digital messages from and transmit reversedigital messages to a digital power device controller (e.g., the digitalpower device controller 1720 of the load control system 1700 of FIG. 24or the digital power device controller 1820 shown in FIG. 25). Thedigital dimming ballast 1910 is operable to control the intensity of afluorescent lamp 1904 to a desired lighting intensity L_(DES) between alow-end intensity L_(LE) and a high-end intensity L_(HE). The digitaldimming ballast 1910 comprises an RFI filter circuit 1911 and arectifier circuit 1920 that operate in a similar manner as the RFIfilter circuit 310 and the rectifier circuit 320 of the digital dimmingballast 300 shown in FIG. 3B.

The digital dimming ballast 1910 comprises a power converter, e.g., aboost converter 1930, which has an input for receiving a rectifiedvoltage V_(RECT) from the rectifier circuit 1920. The boost converter1930 operates to generate a DC bus voltage V_(BUS) across a buscapacitor C_(BUS) and to improve the power factor of the digital dimmingballast 1910 (e.g., as a PFC circuit). The digital dimming ballast 1910comprises an input capacitor C_(IN) coupled across the input of theboost converter 1930. The digital dimming ballast 1910 also includes aload regulation circuit 1940 comprising an inverter circuit 1942 forconverting the DC bus voltage V_(BUS) to a high-frequency AC voltageV_(INV) and a resonant tank circuit 1944 for coupling the high-frequencyAC voltage V_(INV) generated by the inverter circuit to filaments of alamp 1904 (e.g., in a similar manner as the respective circuits of theload regulation circuit 340 of the digital dimming ballast 300 shown inFIG. 3B).

The digital dimming ballast 1910 comprises a control circuit, e.g., amicroprocessor 1960, for providing a drive control signal V_(DRIVE) tothe inverter circuit 1942 for controlling the magnitude of a lampvoltage V_(L) generated across the fluorescent lamp 1904 and a lampcurrent I_(L) conducted through the lamp in response to a lamp currentfeedback signal V_(FB-IL) generated by a lamp current measurementcircuit 1970 and a lamp voltage feedback signal V_(FB-VL) generated by alamp voltage measurement circuit 1972. The control circuit of thedigital dimming ballast 1910 may alternatively comprise, for example, amicrocontroller, a programmable logic device (PLD), an applicationspecific integrated circuit (ASIC), a field-programmable gate array(FPGA), or any suitable processing device, controller, or controlcircuit. The microprocessor 1960 is coupled to a memory 1962 for storageof the control information of the digital dimming ballast 1910. Thedigital dimming ballast 1910 also comprises a power supply 1964, whichreceives the bus voltage V_(BUS) and generates a DC supply voltageV_(CC) (e.g., approximately five volts) for powering the microprocessor1960, the memory 1962, and the other low-voltage circuitry of theballast.

The digital dimming ballast 1910 also comprises an active load circuit1980 coupled across the output of the RFI filter circuit 1911. Theactive load circuit 1980 comprises a threshold detect circuit 1982 and acurrent sink circuit 1984, which is coupled to the RFI filter circuit1911 via two diodes D1986, D1988. The active load circuit 1980 operatesto provide a path for a charging current of a power supply of a digitalpower device controller (e.g., the charging current I_(CHRG) of thepower supply 1821 of the digital power device controller 1820). Theactive load circuit 1980 may provide the path for the charging currentI_(CHRG) in a similar manner as the active load circuit 1490 shown inFIG. 21. The current sink circuit 1984 limits the magnitude of an activeload current conducted through the active load circuit 1980 to less thanor equal to a second current limit I_(LIMIT2), which is greater than thefirst current limit I_(LIMIT1) of the digital ballast controller 1820(e.g., approximately 200 milliamps).

The threshold detect circuit 1982 provides a current sink enable controlsignal V_(CS-EN) to the current sink circuit 1984 for enabling anddisabling the current sink circuit in response to the magnitude of thecontrol-hot voltage V_(CH). The threshold detect circuit 1980 isresponsive to the differential voltage between the control-hot terminalCH and the neutral terminal N of the digital dimming ballast 1910. Thethreshold detect circuit 1980 enables the current sink circuit 1984 whenthe magnitude of the control-hot voltage V_(CH) drops below a fallingthreshold V_(TH-F) (e.g., approximately 10 volts), i.e., at the end ofeach half-cycle. The threshold detect circuit 1982 disables the currentsink circuit 1984 when the magnitude of the control-hot voltage V_(CH)rises above a rising threshold V_(TH-R) (e.g., approximately 20 volts),i.e., when the triac 1810 of the digital power device controller 1820 isrendered conductive. Accordingly, when the triac 1810 of the digitalpower device controller 1820 is non-conductive and the current sinkcircuit 1984 is enabled, the active load circuit 1980 is able to conductthe active load current and the magnitude of the control-hot voltageV_(CH) across the power devices is approximately zero volts.

The active load circuit 1980 is also coupled to a control circuit, e.g.,a microprocessor 1960, of each digital dimming ballast 1910. Thethreshold detect circuit 1980 provides a received forward communicationsignal V_(F-RX) to the microprocessor 1960, such that the microprocessoris able to decode the digital information stored in the timing edges ofthe control-hot voltage V_(CH) (as described above with reference toFIGS. 1-23). For example, the threshold detect circuit 1980 may drivethe received forward communication signal V_(F-RX) high when themagnitude of the control-hot voltage V_(CH) rises above the risingthreshold V_(TH-R) (i.e., approximately 20 volts), and drives thereceived forward communication signal V_(F-RX) low when the magnitude ofthe control-hot voltage V_(CH) drops below the falling thresholdV_(TH-F) (i.e., approximately 10 volts).

The microprocessor 1960 is also coupled to the current sink circuit 1984for overriding the control of the threshold detect circuit 1982 toenable and disable the current sink circuit. Specifically, themicroprocessor 1960 generates a transmit reverse communication signalV_(R-TX), which is representative of the reverse digital messages to betransmitted to the digital power device controller 1720. Themicroprocessor 1960 is able to enable the current sink circuit 1984 whenthe triac 1810 of the digital power device controller 1720 isnon-conductive to cause the magnitude of the control-hot voltage V_(CH)to be approximately zero volts and the magnitude of the controller-dropvoltage V_(CD) to be equal to approximately the magnitude of the ACmains line voltage. The microprocessor 1960 is able to disable thecurrent sink circuit 1984 when the triac 1810 of the digital powerdevice controller 1720 is non-conductive to cause the magnitude of thecontrol-hot voltage V_(CH) to increase above zero volts and themagnitude of the controller-drop voltage V_(CD) to decrease.Accordingly, the microprocessor 1960 is able to control the magnitude ofthe controller-drop voltage V_(CD) when the triac 1810 of the digitalpower device controller 1720 is non-conductive to transmit the reversedigital messages to the digital power device controller. As previouslymentioned, the triac 1810 of the digital power device controller 1720operates to swallow the reverse digital messages, such that the reversedigital messages do not interfere with other control devices that may becoupled to the AC power source 102.

FIG. 27 is a simplified schematic diagram of an example power converter2030 for an electronic ballast (e.g., the boost converter 1930 of thedigital dimming ballast 1910 shown in FIG. 26). The power converter 2030is controlled by a control circuit, e.g., a microprocessor 2060, whichmay be the control circuit 1960 of the digital dimming ballast 1910. Theboost converter 2030 comprises an input that is coupled to the DCterminals of a rectifier circuit 2020 (e.g., the rectifier circuit 1920)for receiving an input voltage V_(IN) (e.g., the rectified voltageV_(RECT)). For example, the rectifier circuit 2020 is shown as afull-wave bridge rectifier in FIG. 27. An input capacitor C_(IN) iscoupled across the input of the boost converter 2030 and may have acapacitance of, for example, approximately 0.22 μF. When the triac of adigital power device controller that is coupled to the digital dimmingballast 1910 (e.g., the triac 1810 of the digital power devicecontroller 1820) is conductive, the power converter 2030 operates in aboost mode to generate a DC bus voltage V_(BUS) from the input voltageV_(IN) (e.g., as a boost converter) and to improve the power factor ofthe digital dimming ballast 1910 (in a similar manner as the boostconverter 330 of the digital dimming ballast 300 shown in FIG. 3B).

The power converter 2030 comprises an inductor L2040, which receives theinput voltage V_(IN) from the rectifier circuit 2020, conducts aninductor current I_(L), and has an inductance L₂₁₀ of, for example,approximately 0.81 mH. The inductor L2040 is coupled to the buscapacitor C_(BUS) via a diode D2042. A power switching device, e.g., afield-effect transistor (FET) Q2044 is coupled in series electricalconnection between the junction of the inductor L2040 and the diodeD2042 and circuit common, and is controlled to be conductive andnon-conductive, so as to generate the bus voltage V_(BUS) across the buscapacitor C_(BUS). The FET Q2044 could alternatively be implemented witha bipolar junction transistor (BJT), an insulated-gate bipolartransistor (IGBT), or any suitable transistor. A resistor divider iscoupled across the bus capacitor C_(BUS) and comprises two resistors82046, 82048, which have, for example, resistances of approximately 1857kΩ and 10 kΩ, respectively. The microprocessor 2060 receives a busvoltage feedback signal V_(B-FB), which is generated at the junction ofthe resistors 82046, R2048 and has a magnitude that is representative ofthe magnitude of the bus voltage V_(BUS).

The microprocessor 2060 is coupled to the gate of the FET Q2044 of thepower converter 2030 for directly controlling the FET Q2044 to beconductive and non-conductive to selectively charge and discharge theinductor L2040 and generate the bus voltage V_(BUS) across the buscapacitor C_(BUS). The power converter 2030 comprises a FET drivecircuit 2050, which is coupled to a gate of the FET Q2044 for renderingthe FET conductive and non-conductive in response to a bus voltagecontrol signal V_(B-CNTL) received from the microprocessor 2060. Themicroprocessor 2060 controls the bus voltage control signal V_(B-CNTL)to control how long the FET Q2044 is rendered conductive and thus adjustthe magnitude of the bus voltage V_(BUS).

The power converter 2030 also comprises an over-current protectioncircuit 2070 that generates an over-current protection signal V_(OCP),which is provided to the microprocessor 2060, such that themicroprocessor is able to render the FET Q2044 non-conductive in theevent of an over-current condition in the FET. The over-currentprotection circuit 2070 comprises a sense resistor 82072 that is coupledin series with the FET Q2044 and has a resistance of, for example,approximately 0.24Ω. The voltage generated across the sense resistorR2072 is coupled to the base of an NPN bipolar junction transistor Q2074via a resistor 82075 (e.g., having a resistance of approximately 1 kΩ).The base of the transistor Q2074 is also coupled to circuit commonthrough a capacitor C2076 (e.g., having a capacitance of approximately470 pF). The collector of the transistor Q2074 is coupled to the DCsupply voltage V_(CC) through a resistor 82078 (e.g., having aresistance of approximately 6.34 kΩ). The over-current protection signalV_(OCP) is generated at the junction of the transistor Q2074 and theresistor R2078. When the voltage across the sense resistor 82072 exceedsa predetermined over-current threshold voltage (i.e., as a result of anover-current condition in the FET Q2044, e.g., approximately 10 amps),the transistor Q2074 is rendered conductive, thus pulling the magnitudeof the over-current protection signal V_(OCP) down towards circuitcommon, such that the microprocessor 2060 renders the FET Q2044non-conductive.

The power converter 2030 further comprises a zero-current detect circuit2080, which generates a zero-current feedback signal V_(B-ZC) when themagnitude of the voltage induced by the inductor L2040 collapses toapproximately zero volts to indicate when the magnitude of the inductorcurrent I_(L) is approximately zero amps. The zero-current detectcircuit 2080 comprises a control winding 2082 that is magneticallycoupled to the inductor L2040. The control winding 2082 is coupled inseries with two resistors 82084, 82085, which each have, for example,resistances of approximately 22Ω. The junction of the resistor R2084,82085, is coupled to the base of an NPN bipolar junction transistorQ2086. The collector of the transistor 2086 is coupled to the DC supplyvoltage V_(CC) through a resistor R2088 (e.g., having a resistance ofapproximately 22 kΩ), such that the zero-current feedback signalV_(B-ZC) is generated at the collector of the transistor. When thevoltage across the inductor L2040 is greater than approximately zerovolts, a voltage is produced across the control winding 2082 and thetransistor Q2086 is rendered conductive, thus driving the zero-currentfeedback signal V_(B-ZC) down towards circuit common. When the magnitudeof the inductor current I_(L) drops to approximately zero amps, thetransistor Q2086 is rendered non-conductive and the zero-currentfeedback signal V_(B-ZC) is pulled up towards the DC supply voltageV_(CC).

As previously mentioned, the power converter 2030 may be part of thedigital dimming ballast 1910, which may be controlled by the digitalpower device controller 1820 shown in FIG. 25. When the triac 1810 ofthe digital power device controller 1820 is non-conductive (i.e., themagnitude of the control-hot voltage V_(CH) is approximately zero voltswith respect to neutral), the digital dimming ballast 1910 is operableto control the current sink circuit 1984 to control the magnitude of thecontroller-drop voltage V_(CD) and transmit the reverse digital messagesto the digital power device controller. However, if the magnitude of theinput voltage V_(IN) across the input capacitor C_(IN) is low (e.g.,approximately zero volts) when the microprocessor 1960 is trying toincrease the magnitude of the control-hot voltage V_(CH) to thusdecrease the magnitude of the controller-drop voltage V_(CD), themagnitude of the control-hot voltage V_(CH) may increase more slowlythan desired due to the input capacitor C_(IN) charging. This slowchange in the magnitude of the control-hot voltage V_(CH) and thus thecontroller-drop voltage V_(CD) can cause communication errors,particularly, when there are many digital dimming ballasts connected tothe digital power device controller 1820. In addition, if the magnitudeof the input voltage V_(IN) across the input capacitor C_(IN) is low(i.e., approximately zero volts) when the digital power devicecontroller 1820 renders the triac 1810 conductive each half-cycle of thecontrol-hot voltage V_(CH), the input capacitor C_(IN) may conduct acharging current having a large magnitude (e.g., approximately one amp),which can cause increased power dissipation (i.e., losses) in theelectrical components of the digital power device controller 1820 andthe digital dimming ballast 1910.

Therefore, when the magnitude of the control-hot voltage V_(CH) isapproximately zero volts each half-cycle (i.e., when the triac 1810 ofthe digital power device controller 1820 is non-conductive), themicroprocessor 2060 is able to control the power converter 2030 tooperate in a buck mode to charge the input capacitor C_(IN) from the busvoltage V_(BUS) (e.g., to operate in a reverse direction as a buckconverter). Specifically, the power converter 2030 further comprisesanother FET Q2090 coupled in series with a diode D2092, with the seriescombination of the FET Q2090 and the diode D2092 coupled in parallel thediode D2042. The microprocessor 2060 is coupled to the gate of the FETQ2090 through a FET drive circuit 2094 for selectively rendering the FETconductive and non-conductive. A resistor divider is coupled across theinput capacitor C_(IN) and comprises two resistors R2096, 82098, whichhave, for example, resistances of approximately 1857 kΩ and 10 kΩ,respectively. The microprocessor 2060 receives an input voltage feedbacksignal V_(IN-FB), which is generated at the junction of the resistorR2096, 82098 and has a magnitude that is representative of the magnitudeof the input voltage V_(IN). The FET drive circuits 2050, 2094 could beimplemented as the low-side and high-side drive circuits, respectively,of a single half-bridge driver IC.

When the microprocessor 2060 renders the FET Q2090 conductive, theinductor L2040 conducts the inductor current I_(L) from the buscapacitor C_(BUS) to the input capacitor C_(IN), and the magnitude ofthe inductor current I_(L) increases. When the FET Q2090 isnon-conductive, the inductor L2040 continues to conduct the inductorcurrent I_(L) through the body diode of the FET Q2044, and the magnitudeof the inductor current I_(L) decreases. Accordingly, the microprocessor2060 is able to control the FET Q2090 to operate the power converter2030 as a buck converter to charge the input capacitor C_(IN) when thetriac 1810 of the digital power device controller 1820 isnon-conductive. For example, the microprocessor 2060 may be operable tocharge the input capacitor C_(IN), such that the magnitude of the inputvoltage V_(IN) is approximately equal to the magnitude of thecontrol-hot voltage V_(CH) when the triac 1810 is rendered conductive.Specifically, the microprocessor 2060 may be operable to charge themagnitude of the input voltage V_(IN) to, for example, approximately 100volts. Accordingly, the difference between the magnitude of thecontrol-hot voltage V_(CH) and the magnitude of the input voltage V_(IN)is minimized, such that the input capacitor C_(IN) does not conduct muchcharging current when the triac 1810 is rendered conductive. Inaddition, the microprocessor 2060 may be operable to over-charge theinput capacitor C_(IN) while the triac 1810 is non-conductive, such thatthe magnitude of the input voltage V_(IN) is greater than the magnitudeof the control-hot voltage V_(CH) when the triac 1810 is renderedconductive.

While not shown in the figures of the present application, the two-wireline-voltage occupancy sensor 1770 may have similar functional blocks asthe digital dimming ballast 1910 shown in FIG. 26. For example, thetwo-wire line-voltage occupancy sensor 1770 may have a microprocessorand an active load circuit (similar to the active load circuit 1980 ofthe digital dimming ballast 1910), such that the two-wire line-voltageoccupancy sensor is able to receive forward digital messages andtransmit reverse digital messages. However, rather than including a loadregulation circuit 1940, the two-wire line-voltage occupancy sensor 1770may comprise an internal occupancy detection circuit for detecting theoccupancy and vacancy conditions in the space around the occupancysensor. The two-wire line-voltage occupancy sensor 1770 may be operableto transmit reverse digital messages including information regardingoccupancy and vacancy conditions detected by the occupancy detectioncircuit. Alternatively, a two-wire line-voltage daylight sensor (notshown) could comprise a microprocessor, an active load circuit, and aninternal photosensitive circuit for measuring the total light levelaround the daylight sensor.

FIG. 28A is a simple diagram of a “forward” digital message 2000 and a“reverse” digital message 2002. For example, the forward digital message2000 may be transmitted by the digital power device controller 1720 tothe power devices of the load control system 1700 of FIG. 24. Thereverse digital message 2002 may be transmitted by one of the powerdevices of the load control system 1700 to the digital power devicecontroller 1720. The forward digital message 2000 may comprise, forexample, a command for the digital dimming ballasts 1710 to control thelamps 1704 or a query for the power devices to report a state or level.The reverse digital message 2002 immediately follows the forward digitalmessage 2000 and may comprise, for example, a response or answer to aquery from the forward digital message (e.g., a simple 1-bit response,such as, “yes” or “no”). For example, queries transmitted by the digitalballast controller 1720 may comprise yes-or-no questions, such as, “Doyou have a lamp fault condition?” (transmitted to the digital dimmingballasts 1710) and “Have you detected an occupied condition?”(transmitted to the two-wire line-voltage occupancy sensor 1770). Theforward digital message 2000 may extend, e.g., for approximately 10 linecycles, while the reverse digital message 2002 may extend, e.g., forapproximately 1.5 line cycles.

The digital power device controller 1720 may be operable to set thevalues of the offset time periods T_(OS1), T_(OS2), T_(OS3), T_(OS4) inresponse to the measured line-voltage time period T_(LC). The digitalpower device controller 1720 may update the first offset time periodT_(OS1) to be equal to half of the measured line-cycle time T_(LC) andthe other offset time periods T_(OS2), T_(OS3), T_(OS4) to be longerthan the first offset time period T_(OS1) by 100, 200, and 300microseconds, respectively, i.e.,

T _(OS1) =T _(LC)/2;

T _(OS2) =T _(OS1) +ΔT _(OS);

T _(OS3) =T _(OS1)+2·ΔT _(OS); and

T _(OS4) =T _(OS1)+3·ΔT _(OS)

where ΔT_(OS) is approximately 100 microseconds.The power devices may be operable to measure the line-voltage timeperiod T_(LC) from the start pattern transmitted by the digital powerdevice controller 1720.

FIG. 28B is a simple timing diagram of a control-hot voltage (e.g., thecontrol-hot voltage V_(CH) generated by the digital power devicecontroller 1720) showing an example start pattern. As shown in FIG. 28B,the digital power device controller 1720 is operable to transmit thestart pattern by rendering the triac 1810 conductive to generate areference edge during a first half-cycle, rendering the triac 1810conductive in a second subsequent half-cycle at the start symbol timeperiod T_(START) from the reference edge in the first half-cycle, andthen rendering the triac conductive after the line-voltage time periodT_(LC) from the reference edge in the first half-cycle. The start symboltime period T_(START) is unique from and longer than the offset timeperiods T_(OS1)-T_(OS4) used to transmit data to the power devices(e.g., approximately 8.78 milliseconds given a 60 Hz line frequency).The power devices are operable to measure the line-voltage time periodT_(LC) (from the reference edge in the first half-cycle to the edge inthe third half-cycle of the start pattern), and to update the offsettime periods T_(OS1), T_(OS2), T_(OS3), T_(OS4) from the measuredline-voltage time period T_(LC). After transmitting the start pattern,the digital power device controller 1720 is operable to immediatelybegin transmitting data in the next half-cycle by generating a referenceedge in the next half-cycle and data edges in the subsequent half-cyclesas shown in FIG. 28B. The power devices are operable to use the updatedoffset time periods T_(OS1), T_(OS2), T_(OS3), T_(OS4) to decode thedata of the forward digital message.

FIGS. 29A and 29B are simple timing diagrams (e.g., of the control-hotvoltage V_(CH) and the controller-drop voltage V_(CD) of the loadcontrol system 1700 of FIG. 24) showing example reverse data patterns ofa reverse digital message. Particularly, the simple reverse digitalmessages may comprise a simple “yes” pattern 2004 as shown in FIG. 29Aand a simple “no” pattern 2005 as shown in FIG. 29B. During the firsthalf-cycle of the reverse digital message, the digital power devicecontroller 1720 first generates a reference edge by rendering the triac1810 conductive after the reference edge time period T_(REF) since thelast zero-crossing. During the time between the zero-crossing and thereference edge, the threshold detect circuit 1982 of the active loadcircuit 1980 of each of the power devices enables the current sinkcircuit 1984, such that the magnitude of the controller-drop voltageV_(CD) is approximately equal to the magnitude of the AC mains linevoltage, thus creating a reference pulse 2006 across the digital powerdevice controller 1720.

During the second half-cycle of the reverse digital message, the digitalpower device controller 1720 maintains the triac 1810 non-conductiveduring a window time period T_(WIN) during which each of the powerdevices may transmit an ACK pulse 2007 (i.e., an acknowledgement) tosignal to the digital power device controller that each power devicereceived the forward digital message that was transmitted just beforethe reverse digital message. The window time period T_(WIN) starts afterthe first offset time period T_(OS1) (i.e., the length of onehalf-cycle) from the reference edge in the first half-cycle of thereverse digital message as shown in FIGS. 29A and 29B. For example, thewindow time period T_(WIN) may be 400 microseconds long. The triac 1810is rendered conductive at the end of the window time period T_(WIN).

Specifically, each of the power devices may transmit the ACK pulse 2007by disabling the current sink circuit 1984 during the window time periodT_(WIN), such that the magnitude of the controller-drop voltage V_(CC)remains below a reverse communication threshold V_(RC-TH) and may be,for example, reduced to approximately zero volts as shown in FIGS. 29Aand 29B. If all of the power devices receive the forward digital messageand disable the current sink circuits 1984 during the window time periodT_(WIN) in the second half-cycle of the reverse digital message, themagnitude of the controller-drop voltage V_(CC) remains below thereverse communication threshold V_(RC-TH). However, if even one of thepower devices does not receive the forward digital message and does notdisable the current sink circuit 1984 during the window time periodT_(WIN) (i.e., allows the threshold detect circuit 1980 to keep thecurrent sink circuit enabled), the magnitude of the controller-dropvoltage V_(CD) will be greater than the reverse communication thresholdV_(RC-TH) when the triac 1810 is rendered conductive at the end of thewindow time period T_(WIN). Accordingly, the digital power devicecontroller 1720 is operable to determine that all of the power devicesdid not receive the forward digital message and to retransmit theforward digital message after the end of the present reverse digitalmessage.

During the third half-cycle of the simple reverse digital message, thedigital power device controller 1720 once again maintains the triac 1810non-conductive during the window time period T_(WIN). During the windowtime period T_(WIN) of the third half-cycle of the simple reversedigital message, each of the power devices may transmit data in the formof a “yes” or “no” answer (e.g., one bit of data) as shown in the “yes”pattern 2004 in FIG. 29A and the “no” pattern 2005 in FIG. 29B.Specifically, each power device may enable the current sink circuit 1984to transmit a “yes” pulse 2008 and may disable the current sink circuitto transmit a “no” pulse 2009 during the window time period T_(WIN) ofthe third half-cycle. If only one power device transmits a “yes” pulse2008, the magnitude of the controller-drop voltage V_(CS) will riseabove the reverse communication threshold V_(RC-TH) during the windowtime period T_(WIN) of the third half-cycle. However, all of the powerdevices need to transmit “no” pulses 2009 for the magnitude of thecontroller-drop voltage V_(CS) to remain below the reverse communicationthreshold V_(RC-TH) during the window time period T_(WIN) of the thirdhalf-cycle. Therefore, the digital power device controller 1720 is onlyable to determine if all of the power devices transmitted “no” patterns2005 or at least one of the power devices transmitted a “yes” pattern2004.

As previously mentioned, the digital power device controller 1720 isoperable to assign link addresses to the power devices during thecommissioning procedure of the two-way load control system 1700. Forexample, the digital power device controller 1720 may be operable totransmit a broadcast forward digital message (e.g., having the question“Do you need an address?”) to all of the power devices. If at least oneof the power devices answers with a “yes” pattern 2004, the digitalpower device controller 1720 may perform a binary search routine todetermine the serial number of the at least one unaddressed powerdevice, and then may assign the unique link address to the power devicehaving that serial number. Alternatively, the power devices may beoperable to produce a 24-bit random number (which may be seeded usingthe serial number) and may use the random number during the binarysearch routine (rather than the serial number).

During the binary search routine, the digital power device controller1720 may be operable to transmit a broadcast forward digital message(e.g., having the question “Is your serial number greater than thenumber N_(BIN-SRCH)?”); and each of the unaddressed ballasts may respondby transmitting “yes” or “no” patterns 2004, 2005. For example, theinitial value of the number N_(BIN-SRCH) may be approximately half ofthe possible range of serial numbers for the digital power devicecontroller 1720. The digital power device controller 1720 may beoperable to transmit the binary search forward digital message (whileupdating the value of the number N_(BIN-SRCH)) and receive “yes” or “no”patterns 2004, 2005 from the power devices until only one power deviceis identified. The identified power device can then transmit its serialnumber to the digital power device controller 1720 and the digital powerdevice controller can transmit the unique link address to the powerdevice. The digital power device controller 1720 can then retransmit thebroadcast forward digital message having the question “Do you need anaddress?” to determine if any more power devices need link addresses,and then perform the binary search routine again if needed. Once all ofthe power devices have been assigned link addresses, the digital powerdevice controller 1720 is operable to exit the addressing mode, and maythen use the assigned link addresses to transmit forward digitalmessages to the power devices.

FIGS. 30-33 show example flowcharts executed by a control circuit of adigital power device controller (e.g., the microprocessor 1814 of thedigital power device controller 1720, 1820) to transmit forward digitalmessages and receive reverse digital messages. The digital power devicecontroller 1820 may be operable to transmit the forward digital messagesto the power devices in a similar manner as described above withreference to FIGS. 16-19, i.e., each forward data pattern has two dataedges. The digital power device controller 1820 generates a referenceedge at the beginning of each forward data pattern 2000 during forwardcommunication, and at the beginning of each reverse data pattern 2002during reverse communication. Accordingly, the microprocessor 1814 ofthe digital power device controller 1820 executes a zero-crossingprocedure (e.g., the zero-crossing procedure 600 as described above withreference to FIG. 11) at the zero-crossing of each half-cycle. Themicroprocessor 1814 sets a timer interrupt for an interrupt time equalto a present value t_(TIMER) of the timer plus the reference time periodT_(REF) at step 614 only if the variable m is equal to zero at step 612at the present zero-crossing to thus generate a reference edge at thetimer interrupt in the first half-cycle of each forward and reverse datapattern.

FIG. 30 is a simplified flowchart of a timer interrupt procedure 2100that is executed by the microprocessor 1814 of the digital power devicecontroller 1820. The microprocessor 1814 may execute the timer interruptprocedure 2100 when the value of the timer equals the set interrupt timeat step 2110, for example, as set during the zero-crossing procedure600. During the timer interrupt procedure 2100, the microprocessor 1814will execute either a forward transmitting procedure 2200 or a reversereceiving procedure 2300. The microprocessor 1814 uses a TX Flag to keeptrack of when the digital power device controller 1820 is presentlytransmitting a forward digital message to the power devices, and uses anRX Flag to keep track of when the digital power device controller ispresently receiving a reverse digital message from the power devices.

If the variable m is equal to zero at step 2112 (i.e., a reference edgeis to be generated during the present half-cycle), the microprocessor1814 sets a base time t₀ equal to the present value of the timer at step2114. If the variable m is not equal to zero at step 2112, themicroprocessor 1814 sets the base time t₀ equal to the base time t₀ fromthe previous half-cycle plus the first offset time period T_(OS1) (i.e.,the length of one half-cycle) at step 2116. If the TX Flag is set atstep 2118, the microprocessor 1814 executes the forward transmittingprocedure 2200, and the timer interrupt procedure 2100 exits. If the RXFlag is set at step 2120, the microprocessor 1814 executes the reversereceiving procedure 2300, before the timer interrupt procedure 2100exits. If neither the TX Flag nor the RX Flag is set at steps 2118,2120, the microprocessor 1814 executes the forward transmittingprocedure 2200 since the digital power device controller 1820 continuesto generate reference and data edges (as if the digital ballastcontroller was continuously transmitting bits “00”) when the digitalpower device controller is not transmitting or receiving digitalmessages.

FIG. 31 is a simplified flowchart of the forward transmitting procedure2200 that is executed by the microprocessor 1814 of the digital powerdevice controller 1820 at the timer interrupts when the TX Flag is setin the timer interrupt procedure 2100. The microprocessor 1814 firstdrives the switch control voltage V_(SW) high at step 2210 to render thecontrollable switching circuit 1860 conductive and then drives the drivevoltage V_(DR) high at step 2212 to render the FET Q1852 of the gatecoupling circuit 1850 conductive to thus render the triac 1810conductive. If the variable m is equal to the number N_(DP) of dataedges in each forward data pattern (i.e., two) indicating the end of thepresent forward data pattern at step 2214, the microprocessor 1814 setsthe variable m equal to zero at step 2216. If the variable m is notequal to the number N_(DP) of data edges in each forward data pattern atstep 2214, the microprocessor 1814 increments the variable m by one atstep 2218.

If the digital power device controller 1820 is not finished transmittingthe present forward digital message at step 2220, the microprocessor1814 determines if there is a higher priority message to transmit atstep 2222. If the microprocessor 1814 has a higher priority message totransmit and should interrupt the digital message that is presentlybeing transmitted at step 2222, the microprocessor clears the lastmessage from the TX buffer at step 2224 and sets an Interrupt MSG Flagat step 2226, before the forward transmitting procedure 2200 exits. Ifthere is not a higher priority message to transmit at step 2222 and thevariable m is not equal to zero at step 2228, the microprocessor 1814executes a data edge procedure (e.g., the data edge procedure 800 asdescribed above with reference to FIG. 13), before the forwardtransmitting procedure 2200 exits. During the data edge procedure 800,the microprocessor 1814 sets the interrupt time of the next timerinterrupt equal to the base time t₀ plus the start symbol time periodT_(START) at step 816 if the microprocessor 1814 is presentlytransmitting the first bit of a start pattern, and sets a timerinterrupt for the interrupt time of the next timer interrupt equal tothe base time t₀ plus the first offset time period T_(OS1) at step 816if the microprocessor 1814 is presently transmitting the second bit ofthe start pattern. The start symbol time period T_(START) may be equalto approximately 8.68 milliseconds (i.e., 450 microseconds longer thanthe first offset time period T_(OS1)).

However, if the digital power device controller 1820 just transmittedthe last two bits of the present forward digital message in the dataedge procedure 800 (i.e., it is the end of the forward digital message)at step 2220, the microprocessor 1814 then determines if a response tothe forward digital message is required based on the nature of thecommand or query in the forward digital message at step 2230. If aresponse is required from the power devices 1710 at step 2230, themicroprocessor 1814 sets the RX Flag at step 2232 and clears the TX Flagat step 2234, before the forward transmitting procedure 2200 exits. If aresponse is not required at step 2230, the microprocessor 1814 clearsthe last forward digital message from the TX buffer at step 2236. Ifthere are not more forward digital messages in the TX buffer at step2238, the microprocessor 1814 clears the TX Flag at step 2234 and theforward transmitting procedure 2200 exits.

FIG. 32 is a simplified flowchart of the reverse receiving procedure2300 that is executed by the microprocessor 1814 of the digital powerdevice controller 1820 at the timer interrupts when the RX Flag is setin the timer interrupt procedure 2100. If the variable m is equal tozero at step 2310, the microprocessor 1814 drives the switch controlvoltage V_(SW) high at step 2312 to render the controllable switchingcircuit 1860 conductive and then drives the drive voltage V_(DR) high atstep 2212 to render the FET Q1852 of the gate coupling circuit 1850conductive to thus render the triac 1810 conductive. If the variable mis not equal to the number N_(DP) of data edges in each reverse datapattern (i.e., two) at step 2316, the microprocessor 1814 increments thevariable m by one at step 2318 and sets the interrupt time of the nexttimer interrupt equal to the base time t₀ (as determined at step 2114 ofthe timer interrupt procedure 2100) plus the first offset time periodT_(OS1) at step 2320, before the reverse receiving procedure 2300 exits.

When the timer interrupt occurs and the reverse receiving procedure 2300is executed once again, the variable m will not be equal to one at step2310 and the microprocessor 1814 prepares to receive data of a reversedigital message from the power devices during the window time periodT_(WIN). Specifically, the microprocessor 1814 drives the current-limitcontrol signal V_(CL) low at step 2322 to render the current-limitcircuit 1830 non-conductive to prevent the power supply 1821 fromcharging. The microprocessor 1814 then drives the switch control voltageV_(SW) low at step 2324 to render the controllable switching circuit1860 non-conductive and then drives the drive voltage V_(DR) high atstep 2326 to render the FET Q1852 of the gate coupling circuit 1850conductive. Since the controllable switching circuit 1860 isnon-conductive, the triac 1810 is not rendered conductive. However, thecurrent sink circuit 1984 of each of the power devices is able toconduct the active load current through the FET Q1852.

The microprocessor 1814 then waits until the end of the window timeperiod T_(WIN) at step 2328. When the present value t_(TIMER) of thetimer is equal to the base time t₀ plus the length of the window timeperiod T_(WIN) at step 2328, the microprocessor 1814 executes a receivedata procedure 2400, which will be explained in greater detail belowwith reference to FIG. 33. The microprocessor 1814 then drives theswitch control voltage V_(SW) high at step 2330 to render thecontrollable switching circuit 1860 conductive, such that the triac 1810is rendered conductive at the end of the window time period T_(WIN). Themicroprocessor 1814 also drives the current-limit control signal V_(CL)high at step 2332, such that the power supply 1821 will be able to begincharging again when the triac 1810 is non-conductive at the beginning ofthe next half-cycle. If the variable m is not equal to the number N_(DP)of data edges in each reverse data pattern at step 2316, themicroprocessor 1814 increments the variable m by one at step 2318 andsets the interrupt time of the next timer interrupt equal to the basetime t₀ plus the first offset time period T_(OS1) at step 2320, beforethe reverse receiving procedure 2300 exits. When the variable m is equalto the number N_(DP) of data edges in each reverse data pattern at step2316, the microprocessor 1814 sets the variable m equal to zero at step2334 and the reverse receiving procedure 2300 exits.

FIG. 33 is a simplified flowchart of the receive data procedure 2400,which is executed by the microprocessor 1814 at the end of the windowtime period T_(WIN) when the digital power device controller 1820 isreceiving a reverse digital message. If the variable m is equal to oneat step 2410 (i.e., it is the second half-cycle of the reverse digitalmessage 2002) and the magnitude of the reverse communication receivesignal V_(R-RX) is not high at step 2412 (i.e., indicating that themagnitude of the controller-drop voltage V_(CD) is below the reversecommunication threshold V_(RC-TH) at the end of the window time periodT_(WIN)), the microprocessor 1814 determines that acknowledgements havebeen received from all of the power devices coupled to the digital powerdevice controller 1820. The microprocessor 1814 then clears the lastforward digital message from the TX buffer at step 2414 and the receivedata procedure 2400 exits. If the magnitude of the reverse communicationreceive signal V_(R-RX) is high at step 2412 (i.e., indicating that themagnitude of the controller-drop voltage V_(CD) is above the reversecommunication threshold V_(RC-TH) at the end of the window time periodT_(WIN)), the microprocessor 1814 determines that at least one of thepower devices did not transmit an acknowledgement and sets a RETRY Flagat step 2416, before the receive data procedure 2400 exits.

If the variable m is equal to two at step 2418 (i.e., it is the thirdhalf-cycle of the reverse digital message 2002) and the magnitude of thereverse communication receive signal V_(R-RX) is high at step 2420, themicroprocessor 1814 sets the value of the received data RX_Data equal to“Yes” (or a logic one) at step 2422. If the magnitude of the reversecommunication receive signal V_(R-RX) is low at step 2420, themicroprocessor 1814 sets the value of the received data RX_Data equal to“No” (or a logic zero) at step 2424. After setting the value of thereceived data RX_Data at step 2422, 2424, the microprocessor 1814 clearsthe RX Flag at step 2426 and the receive data procedure 2400 exits.

FIGS. 34-38 show example flowcharts executed by a control circuit of apower device (e.g., the microprocessor 1960 of the digital dimmingballast 1710, 1910) to receive forward digital messages and transmitreverse digital messages. Specifically, FIG. 34 is a simplifiedflowchart of a zero-crossing procedure 2500 executed periodically by themicroprocessor 1960 of the digital dimming ballast 1710 when themagnitude of the control-hot voltage V_(CH) drops below the fallingthreshold V_(TH-F) at step 2510, i.e., at the beginning of eachhalf-cycle. During the zero-crossing procedure 2500, the microprocessor1960 renders the FET Q2044 non-conductive at step 2512 and beginscontrolling the FET Q2090 to charge the input capacitor C_(IN) from thebus voltage V_(BUS) at step 2514, before the zero-crossing procedure2500 exits.

FIG. 35 is a simplified flowchart of a rising edge procedure 2600executed by the microprocessor 1960 or 2060 of each digital dimmingballast 1910 when the magnitude of the control-hot voltage V_(CH) risesabove the rising threshold V_(TH-R) at step 2610. The microprocessor1960 uses an RX Flag to keep track of when the digital dimming ballast1910 is presently receiving a forward digital message from the digitalpower device controller 1820, and uses a TX Flag to keep track of whenthe digital dimming ballast is presently transmitting a reverse digitalmessage to the digital power device controller. The microprocessor 1960first sets the rising edge time t_(E) equal to the present valuet_(TIMER) of the timer at step 2612. The microprocessor 1960 thenrenders the FET Q2090 non-conductive at step 2614 and begin controllingthe FET Q2044 to charge the bus capacitor C_(BUS) from the input voltageV_(IN) at step 2616.

If the TX Flag is not set at step 2618, the microprocessor 1960 monitorsthe control-hot voltage V_(CH) to determine if the digital power devicecontroller 1720 has transmitted a start pattern to start a new forwarddigital message (as described above). The microprocessor 1960 determinesthe last two time periods T₁, T₂ between the rising edges of thecontrol-hot voltage V_(al) at step 2620 by setting the first time periodT₁ equal to the previous second time period T₂ and setting the secondtime period T₂ equal to the rising edge time t_(E) minus a previousrising edge time t_(E-PREV). Next, the microprocessor 1960 determines ifthe last two time periods T₁, T₂ between the rising edges of thecontrol-hot voltage V_(al) are approximately equal to time periodsT_(START) and T_(LC)−T_(START), respectively. Specifically, if the firstperiod T₁ is not within the default tolerance ΔT_(OS) of the startsymbol offset time period T_(START) at step 2622, and the second periodT₂ is not within the default tolerance ΔT_(OS) of the difference betweenthe line-cycle time period T_(LC) and the start symbol offset timeperiod T_(START) at step 2624, the microprocessor 1960 determines that astart pattern was not received, and sets the previous rising edge timet_(E-PREV) equal to the present rising edge time t_(E) at 2626. If theRX Flag is not set at step 2628, the rising edge procedure 2600 simplyexits.

If the microprocessor 1960 received a start pattern at steps 2622, 2624,the microprocessor 1960 first sets the new values of the time periodsT_(OS1), T_(OS2), T_(OS3), T_(OS4), at step 2630, i.e.,

T _(OS1)=(T ₁ +T ₂)/2;

T _(OS2) =T _(OS1) +ΔT _(OS),

T _(OS3) =T _(OS1)+2·ΔT _(OS); and

T _(OS4) =T _(OS1)+3·ΔT _(OS).

The microprocessor 1960 then clears the RX buffer at step 2632, sets thevariable x to zero at step 2634, and sets the RF Flag at step 2636,before the rising edge procedure 2600 exits. When the RX Flag is set atstep 2628, the microprocessor 1960 executes a forward receivingprocedure 2700, which will be described in greater detail below withreference to FIG. 36. When the TX Flag is set at step 2618, themicroprocessor 1960 executes a reverse transmitting procedure 2800,which will be described in greater detail below with reference to FIG.37.

FIG. 36 is a simplified flowchart of the forward receiving procedure2700 executed by the microprocessor 1960 of each digital dimming ballast1710 when the RX Flag is set during the rising edge procedure 2600. Ifthe variable x is equal to zero at step 2710, the microprocessor 1960determines that the rising edge that was just received is a referenceedge of a forward data pattern, and sets a reference edge time t_(REF-E)equal to the rising edge time t_(E) (from step 2612 of the rising edgeprocedure) at step 2712. If the variable x is not equal to the numberN_(DP) of data edges in each forward data pattern at step 2714, themicroprocessor 1960 increments the variable x by one at step 2716 andthe forward receiving procedure 2700 exits. If the variable x is notequal to zero at step 2710, the microprocessor 1960 determines that therising edge that was just received is a data edge of a forward datapattern, and calculates the measured offset time T_(M-OS) in dependenceupon the variable x at step 2718, i.e.,

T _(M-OS)=(t _(E) −t _(REF-E))−(x−1)*T _(OS1).

The microprocessor 1960 then executes a receive data procedure (e.g.,the receive data procedure 1000 as described above with reference toFIG. 15) to determine the bits of data that are encoded in the measuredoffset time T_(M-OS).

If the MSG-RX Flag is set at step 2720 indicating that a completeforward digital messages has been received (as set at step 1032 of thereceive data procedure 1000), the microprocessor 1960 clears the RX Flagat step 2722. If the received forward digital message requires aresponse at step 2724, the microprocessor 1960 loads a reverse digitalmessage including an appropriate response to the received forwarddigital message into the TX buffer at step 2726 and sets the TX Flag atstep 2728. If the variable x is equal to the number N_(DP) of data edgesin each forward data pattern at step 2714, the microprocessor 1960 setsthe variable x equal to zero at step 2730 and the forward receivingprocedure 2700 exits.

FIG. 37 is a simplified flowchart of the reverse transmitting procedure2800 executed by the microprocessor 1960 of the digital dimming ballast1910 when the TX Flag is set during the rising edge procedure 2600. Ifthe variable x is equal to zero at step 2810 (i.e., it is the firsthalf-cycle of the reverse digital message), the microprocessor 1960 setsthe reference edge time t_(REF-E) equal to the to the rising edge timet_(E) (from step 2612 of the rising edge procedure 2600) at step 2812.If the variable x is not equal to the number N_(DP) of data edges ineach reverse data pattern at step 2814, the microprocessor 1960increments the variable x by one at step 2816 and sets the interrupttime of the next timer interrupt equal to the base time t₀ plus thefirst offset time period T_(OS1) at step 2818, before the reversetransmitting procedure 2800 exits.

At the timer interrupt, the microprocessor 1960 will execute a reversetransmit data procedure 2900 to transmit an ACK pulse 2007 and a “yes”pulse 2008 or a “no” pulse 2009 as will be described in greater detailbelow with reference to FIG. 38. The timer interrupt is timed to occurat the beginning of the window time period T_(WIN) in each of the secondand third half-cycles of the reverse digital message 2002. During thewindow time period T_(WIN), the microprocessor 1960 disables the currentsink circuit 1984. When the triac 1810 of the digital power devicecontroller 1820 is rendered conductive at the end of the window timeperiod T_(WIN), the microprocessor 1960 will execute the rising edgeprocedure 2600 and the reverse transmitting procedure 2800. During thereverse transmitting procedure 2800, when the variable x is not equal tozero at step 2810, the microprocessor 1960 drives the current sinkenable control signal V_(CS-EN) high at step 2820 to enable to thecurrent sink circuit 1984. If the variable x is equal to the numberN_(DP) of data edges in each reverse data pattern at step 2814, themicroprocessor 1960 sets the variable x equal to zero at step 2822 andthe reverse transmitting procedure 2800 exits.

FIG. 38 is a simplified flowchart of the reverse transmit data procedure2900, which is executed by the microprocessor 1960 of the digitaldimming ballast 1910 when the value of the timer equals the setinterrupt time at step 2910. If the variable x is equal to one at step2912 (i.e., it is the second half-cycle of the reverse digital message),the microprocessor 1960 drives the current sink enable control signalV_(CS-EN) low at step 2914 to disable the current sink circuit 1984 andthus transmit an ACK pulse 2007, before the reverse transmit dataprocedure 2900. If the variable x is equal to two at step 2916 (i.e., itis the third half-cycle of the reverse digital message), themicroprocessor 1960 transmits a “yes” pulse 2008 or a “no” pulse 2009.Specifically, if the transmit data TX_Data is “Yes” (i.e., a logic one)at step 2918, the microprocessor 1960 maintains the current sink enablecontrol signal V_(CS-EN) high at step 2920, and clears the TX Flag atstep 2922, before the reverse transmit data procedure 2900 exits. If thetransmit data TX_Data is “No” (i.e., a logic zero) at step 2918, themicroprocessor 1960 drives the current sink enable control signalV_(CS-EN) low at step 2924, and clears the TX Flag at step 2922, beforethe reverse transmit data procedure 2900 exits.

Alternatively, the power devices of the load control system 1700 may beoperable to transmit reverse digital messages that each have multiplebits of data to the digital power device controller 1720. In addition,the power devices may be able to receive the reverse digital messagestransmitted by the other power devices. Therefore, the power devices cantransmit more feedback information to the digital power devicecontroller 1720. For example, the digital dimming ballast 1710 may beoperable to transmit the present lighting intensity of the controlledlamp 1704 or the present power consumption of the ballast. In addition,a line-voltage daylight sensor coupled to the digital power devicecontroller 1720 could transmit the actual total light level measured bythe daylight sensor to the digital power device controller. The digitalpower device controller 1720 may receive information regarding thereliability and robustness of the communications provided with the powerdevices across the circuit wiring 1714.

FIG. 39A is an example diagram of a message structure for a forwarddigital message transmitted by a digital power device controller (e.g.,the digital ballast controller 1720 of the load control system shown inFIG. 24). Each forward digital message may comprise a total numberN_(SM) of bits (e.g., 26 bits). The first four bits comprises a startpattern, which includes a unique start symbol as will be described ingreater detail below with reference to FIG. 8. The start pattern isfollowed by a payload, which may comprise 17 bits. For example, thepayload may comprise the link address of the digital dimming ballast1710 to which the forward digital messages is being transmitted and anintensity level to which the digital dimming ballast 1710 should controlthe respective lamp 1704. The payload may also comprise a query type anda query message. If the forward digital message is being transmitted toupgrade settings or firmware of a power device, the payload may simplycomprise data. Each digital message concludes with five bits that areused to determine if an error occurred during transmission and receptionof the digital message (e.g., a checksum).

FIG. 39B is an example diagram of a forward digital message 3000 and areverse digital message 3002 having multiple bits of data. For example,the forward digital message 3000 may be transmitted from the digitalballast controller 1720 to the power devices and the reverse digitalmessage 3002 may be transmitted from one of the power devices to thedigital ballast controller. The power devices are configured to transmita reverse digital message 3002 in response to receiving a forwarddigital message 3000 from the digital power device controller 1720,e.g., immediately following the forward digital messages as shown inFIG. 39B. Each forward digital message 3000 may include a command or aquery and have a total number N_(FM) of bits that require apredetermined number of line cycles to transmit. The last half-cycle ofthe forward digital message 3000 may comprise a window time periodT_(WIN) for the power devices to transmit an acknowledgement (as will bedescribed in greater detail below). Each reverse digital message 3002may comprise, a total number N_(RM) of bits (e.g., 8 bits), and mayextend for three line cycles. The power devices may also be configuredto transmit a reverse digital message without receiving a forwarddigital message from the digital power device controller 1720.

FIG. 40 is an example timing diagram (e.g., of the control-hot voltageV_(CH) and the controller-drop voltage V_(CD) of the load control system1700 of FIG. 24) showing an example reverse digital message. Asmentioned above, the power devices are operable to transmit an ACK pulse3007 during the last half-cycle of the forward digital message 3000(e.g., such that each forward digital message may require 10.5 linecycles to transmit). The power devices may then immediately begintransmitting data in the first data pattern of the reverse digitalmessage. For example, the power devices may transmit a “logic one” pulse3008 by enabling the current sink circuit 1984 to allow the magnitude ofthe controller-drop voltage V_(CD) to increase above the reversecommunication threshold V_(RC-TH). In addition, the power devices maytransmit a “logic zero” pulse 3009 by disabling the current sink circuit1984 to control the magnitude of the controller-drop voltage V_(CD) toapproximately zero volts.

The power devices may also be operable to receive a reverse digitalmessage (e.g., the reverse digital message shown in FIG. 40) that istransmitted by the other power devices coupled to the digital powerdevice controller 1720. While each power device is transmitting areverse digital message, the power device is further operable todetermine if another power device is also transmitting a reverse digitalmessage at the same time. For example, if the power device istransmitting a “logic zero” pulse 3009, the power device is operable tomonitor the magnitude of the control-hot voltage V_(CH) while the powerdevice has disabled the current sink circuit 1984 to determine ifanother control device is transmitting a “logic one” pulse 3008. If so,the power device ceases transmitting the reverse digital message toallow the other power device to finish transmitting.

The power devices may be operable to transmit reverse digital messageshaving more than the total number N_(RM) of bits (i.e., 8 bits). Forexample, the power devices may be operable to transmit the data of areverse digital message in multiple packets 3002A, 3002B, 3002C as shownin FIG. 39B. After each packet 3002A, 3002B, the digital power devicecontroller 1720 is operable to transmit a continuation pattern (orpacket) 3004, which may be a short pattern that may extend for, e.g.,three half cycles, i.e., equal to the length of a data pattern, but lessthan the length of an entire forward digital message. Each of thepackets 3002A, 3002B, 3002C may comprise a total number N_(RM-PKT) ofbits (e.g., 8 bits). Thus, as shown in FIG. 39B, a total numberN_(RM-TOTAL) of bits of each entire reverse digital message having threepackets 3002A, 3002B, 3002C may be equal to 24 bits. Alternatively, thereverse digital messages may comprise other numbers of packets, suchthat the total number N_(RM-TOTAL) of bits of each entire reversedigital message may equal a different number of bits.

The digital power device controller 1720 is operable to transmit thecontinuation pattern 3004 using an old offset time period T_(OS1-OLD)from the previous packet (e.g., packet 3002A) and a new offset timeperiod T_(OS1-NEW) that will be used in the next packet (e.g., packet3002B). Specifically, the digital power device controller 1720 transmitsthe continuation pattern by generating a reference edge during a firsthalf-cycle, rendering the controllably conductive device conductive in asecond subsequent half-cycle at the old offset time period T_(OS1-OLD)plus the offset period difference ΔT_(OS) (e.g., approximately 100microseconds) from the reference edge in the first half-cycle, and thenrendering the controllably conductive device conductive after two timesthe new offset time period T_(OS1-NEW) from the reference edge in thefirst half-cycle. The continuation pattern allows the power devices tosynchronize the values of the offset time periods T_(OS1), T_(OS2),T_(OS3), T_(OS4) with those being used by the digital power devicecontroller 1720. The power devices are operable to measure theline-cycle time period T_(LC) (i.e., two times the new offset timeperiod T_(OS1-NEW)) from the continuation pattern and update the valuesof the offset time periods T_(OS1), T_(OS2), T_(OS3), T_(OS4) using thenew offset time period T_(OS1-NEW).

One bit of each packet 3002A, 3002B, 3002C may comprise a parity bit forconfirming the integrity of the data of that packet. For example, theparity bit may be set to zero if the number of ones in the packet is anodd number, and may be set to one if the number of zeros in the packetis an even number. If the parity bit of a packet (e.g., the packet3002A) received by the digital power device controller 1720 indicatesthat there may be an error in the packet, the digital power devicecontroller 1720 is operable to transmit a retry pattern (or packet) 3009instead of the continuation pattern 3004 as shown in FIG. 39D. The retrypattern 3009 is a short pattern that may extend for, e.g., three halfcycles, i.e., the length of a data pattern, but may be different thanthe continuation pattern 3004. If a power device receives a retrypattern 3009 after transmitting a packet of a reverse digital message(e.g., the packet 3002A), the power device will retransmit the packet asshown in FIG. 39D. If the second transmission of the packet 3002A isreceived without error, the digital ballast controller 1720 willtransmit the continuation pattern 3004 and the power device willtransmit the next packet 3002B.

The digital power device controller 1720 may also be operable totransmit query commands to which all of the power devices connected tothe digital power device controller 1720 may respond to individually(i.e., at different times), for example, in sequential order based ontheir link addresses. For example, the power devices may each beoperable to transmit a reverse digital message 3002, 3006, 3008 inresponse to a single forward digital message 3000 as shown in FIG. 39E.The digital power device controller 1720 may be operable to transmit thecontinuation pattern 3004 after each reverse digital message 3002, 3006,3008. If the parity bit of one of the reverse digital messages 3002,3006, 3008 indicates that there may be an error in the reverse digitalmessage, the digital power device controller 1720 is operable totransmit the retry pattern 3009 instead of the continuation pattern 3004as shown in FIG. 39F. If a power device receives a retry pattern 3009after transmitting a reverse digital message (e.g., the reverse digitalmessage 3002 shown in FIG. 39F), the power device will retransmit thereverse digital message. If the second transmission of the reversedigital message 3002 is received without error, the digital ballastcontroller 1720 will transmit the continuation pattern 3004 and the nextpower device will transmit the next reverse digital message 3006.

As shown in FIG. 39G, the digital power device controller 1720 may beoperable to transmit multiple-packet forward digital messages (e.g.,having packets 3000A, 3000B) to the power devices, for example, totransmit a firmware upgrade to the power devices. The digital powerdevice controller 1720 may transmit the continuation pattern 3002between the packets 3000A, 3000B of the multiple-packet forward digitalmessage.

In addition, the digital power device controller 1720 may be operable totransmit a start pattern immediately following a reverse digital messageto start a new forward digital message as shown in FIG. 39H. Forexample, the digital power device controller 1720 may be operabletransmit a new forward digital message 3000C after a first packet 3002Aof a reverse digital message (rather than transmitting the continuationpattern 3004 as shown in FIG. 39C). Further, the digital powercontroller 1720 may be operable to start transmitting bits “00” to causethe power devices to do nothing and return to the idle state.

As previously mentioned, the digital power device controller 1720 isoperable to assign link addresses to the power devices during thecommissioning procedure of the two-way load control system 1700. Thepower devices may be operable to randomly generate a random address(which may be the same length as the link addresses). The digital powerdevice controller 1720 may be operable to transmit a broadcast forwarddigital message (e.g., a query message having the question “What is yourrandom address?”) to all of the power devices. The power devices thathave not been assigned a link address may respond to the broadcastmessage by transmitting a reverse digital message including their randomaddress. While transmitting their random address, the power devices areoperable to monitor the magnitude of the control-hot voltage V_(CH) todetermine if another control device is transmitting its random address.Specifically, if a power device is transmitting a “logic zero” pulse3009 of its random address, the power device is operable to monitor themagnitude of the control-hot voltage V_(CH) (while the power device hasdisabled the current sink circuit 1984) to determine if another controldevice is transmitting a “logic one” pulse 3008. If so, the power deviceceases transmitting its random address. Eventually, one power deviceremains transmitting its random address, which is fully received by thedigital power device controller 1720. The digital power devicecontroller 1720 then assigns a new link address to the remaining powerdevice and transmits a forward digital message including the new linkaddress to the power device having the random address that was justreceived. The digital power device controller 1720 may then assign linkaddresses to the other power devices by repeating the process, i.e., bytransmitting a broadcast forward digital message (e.g., a query messagehaving the question “What is your random address?”) to all of the powerdevices.

FIG. 41 is a simplified block diagram of an example digital dimmingballast 3110 that is able to communicate via a circuit wiring, e.g., thecircuit wiring 1714 of the load control system 1700, as well ascommunicate via a wired digital communication link 3116, such as, forexample, a digital addressable lighting interface (DALI) communicationlink. The digital dimming ballast 3110 shown in FIG. 41 is very similarto the digital dimming ballast 1710 shown in FIG. 26. The digitaldimming ballast 3110 comprises a control circuit, e.g., a microprocessor3160, that is operable to receive the forward digital messages and totransmit the reverse digital messages via the circuit wiring 1714. Thedigital dimming ballast 3110 also comprises a digital communicationcircuit 3166 coupled to the microprocessor 3160 for transmitting andreceiving digital messages via the wired communication link 3116. Themicroprocessor 3160 may be operable to automatically detect whetherdigital messages are being received via the circuit wiring 1714 or thewired communication link 3116 to determine the communication medium onwhich the digital dimming ballast 3110 will transmit and receive digitalmessages. Alternatively, both communication mediums could be used totransmit and/or receive digital messages. Additionally or alternatively,the digital communication circuit 3166 could be operable to transmit andreceive digital messages via a wireless link (e.g., radio frequency,infra-red, etc).

FIG. 42 is a simplified block diagram of an example digital dimmingballast 3210 (e.g., one of the digital dimming ballasts of the loadcontrol system 1700 of FIG. 24) that is able to communicate and receivepower via a circuit wiring (e.g., the circuit wiring 1714). The digitaldimming ballast 3210 shown in FIG. 42 is very similar to the digitaldimming ballast 1710 shown in FIG. 26. The digital dimming ballast 3210comprises a boost converter 3230 that receives a rectified voltageV_(RECT) produced across an input capacitor C_(IN) and generates a busvoltage V_(BUS) across a bus capacitor C_(BUS), where the magnitude ofthe bus voltage V_(BUS) is greater than the peak magnitude of therectified voltage V_(RECT). The digital dimming ballast 3210 comprises afirst power supply 3264 (e.g., a buck converter) configured to receivethe bus voltage V_(BUS) and generate a DC supply voltage V_(CC) forpowering a control circuit (e.g., a microprocessor 3260) and the otherlow-voltage circuitry of the ballast. The digital dimming ballast 3210also comprises a second, separate power supply 3265 (e.g., a buckconverter) that also receives the bus voltage V_(BUS), but is coupled tothe input capacitor C_(IN) of the boost converter 3230 (i.e., to therectified voltage V_(RECT)) for charging the input capacitor C_(IN) whenthe magnitude of the control-hot voltage V_(CH) is approximately zerovolts each half-cycle (e.g., when the triac 1810 of the digital powerdevice controller 1820 is non-conductive).

FIG. 43 is a simplified block diagram of an example digital dimmingballast 3310 (e.g., one of the digital dimming ballasts of the loadcontrol system 1700 of FIG. 24) that is able to communicate and receivepower via a circuit wiring (e.g., the circuit wiring 1714). The digitaldimming ballast 3310 shown in FIG. 43 is very similar to the digitaldimming ballast 1710 shown in FIG. 26. The digital dimming ballast 3310comprises a boost converter 3330 that receives a rectified voltageV_(RECT) produced across an input capacitor C_(IN) and generates a busvoltage V_(BUS) across a bus capacitor C_(BUS), where the magnitude ofthe bus voltage V_(BUS) is greater than the peak magnitude of therectified voltage V_(RECT). The digital dimming ballast 3310 comprises apower supply 3364 (e.g., a buck converter) that receives the bus voltageV_(BUS) and has first and second outputs. At the first output, the powersupply 3364 provides a DC supply voltage V_(CC) for powering a controlcircuit (e.g., a microprocessor 3360) and the other low-voltagecircuitry of the ballast. The second output of the power supply 3364 iscoupled to the input capacitor C_(IN) of the boost converter 3330 forcharging the input capacitor C_(IN) when the magnitude of thecontrol-hot voltage V_(CH) is approximately zero volts each half-cycle(e.g., when the triac 1810 of the digital power device controller 1820is non-conductive).

FIG. 44 is a simplified schematic diagram of an example power supply3470 for a load control device (e.g., the power supply 3364 of thedigital dimming ballast 3310 shown in FIG. 43). The power supply 3470receives a bus voltage V_(BUS) that may be generated by a boostconverter 3430 (e.g., the boost converter 3330 of the digital dimmingballast 3310 shown in FIG. 43). The boost converter 3430 comprises aninput for receiving an input voltage V_(IN) (e.g., a rectified voltage)from a rectifier circuit 3420 (e.g., a full-wave bridge rectifier asshown in FIG. 44). An input capacitor C_(IN) is coupled across the inputof the boost converter 3430 and may have a capacitance of, for example,approximately 0.22 μF. The power supply 3470 may comprise a first output3472 for providing a DC supply voltage V_(CC) for powering a controlcircuit (e.g., a microprocessor 3460). The power supply 3364 comprises asecond output 3474 that may be coupled to the input capacitor C_(IN) forcharging the input capacitor when the magnitude of the control-hotvoltage V_(CH) is approximately zero volts. The microprocessor 3460receives an input voltage feedback signal V_(IN-FB) from a resistordivider that is coupled across the input capacitor C_(IN) and includestwo resistors R3476, R3478 (e.g., having resistances of approximately1857 kΩ and 10 kΩ, respectively). The input voltage feedback signalV_(IN-FB) has a magnitude that is representative of the magnitude of theinput voltage V_(IN).

The power supply 3470 is operable to generate the DC supply voltageV_(CC) across a supply capacitor C3480 (e.g., having a capacitance ofapproximately 220 μF). The power supply 3470 comprises a buck converterincluding a power switching device, e.g., a FET Q3482, coupled toreceive the bus voltage V_(BUS), an inductor L3484 (e.g., having aninductance of approximately 680 μH), and diodes D3485, D3486. Theinductor L3484 is coupled between the FET Q3482 and the diode D3486,while the diode D3485 is coupled between circuit common and the junctionof the FET Q3482 and the inductor L3484. The diode D3486 is coupled tothe supply capacitor C3480 through a first controllable switch 3488(e.g., a FET), which may be opened and closed in response to a switchcontrol signal V_(SW-CNTL) generated by the microprocessor 3460. Thepower supply 3470 further comprises a buck control circuit 3489 coupledto the gate of the FET Q3482 for controlling the operation of the buckconverter. The FET Q3482 and the buck control circuit 3489 may beimplemented together in an integrated circuit, e.g., a VIPER16converter, manufactured by STMicroelectronics. The buck control circuit3489 may be referenced to the junction of the FET Q3482 and the inductorL3484.

The power supply 3470 further comprises a feedback circuit 3490configured to receive the supply voltage V_(CC) from the supplycapacitor C3480. The feedback circuit 3490 generates a feedback signalV_(PS-FB), which is coupled to the buck control circuit 3489 through adiode D3495 to charge a capacitor C3496. The buck control circuit 3489is configured to control the operation of the buck converter to generatethe DC supply voltage V_(CC) in response to the voltage generated on thecapacitor C3496 (i.e., in response to the feedback signal V_(PS-FB)).The feedback circuit 3490 comprises a second controllable switch 3492(e.g., a FET or a bipolar junction transistor) and a diode D3494 coupledin parallel with the controllable switch. The microprocessor 3460generates a feedback circuit control signal V_(FB-CNTL) for controllingthe second controllable switch 3492 (i.e., to open and closed theswitch).

The microprocessor 3460 is configured to close the first and secondcontrollable switches 3488, 3492 to allow the buck converter to generatethe DC supply voltage V_(CC) across the supply capacitor C3480. Becausethe second controllable switch 3492 is closed, the magnitude of thefeedback signal V_(PS-FB) is approximately equal to the magnitude of theDC supply voltage V_(CC). When the buck control circuit 3489 renders theFET Q3482 conductive, the inductor L3484 is operable to charge from thebus voltage V_(BUS) and the DC supply voltage V_(CC) increases inmagnitude. When the FET Q3482 is rendered non-conductive, the inductorL3484 is operable to conduct current through the supply capacitor C3480and the diode D3485. At this time, the junction of the source of the FETQ3482 and the inductor L3484 (to which buck control circuit 3489 isreferenced) is one diode drop below circuit common, and the magnitude ofthe voltage across the capacitor C3496 is one diode drop below themagnitude of the feedback voltage V_(PS-FB) (which is approximatelyequal to the magnitude of the supply voltage V_(CC)). Accordingly, thevoltage across the capacitor C3496 is representative of the magnitude ofthe supply voltage V_(CC) when the diode D3485 is conductive. The buckcontrol circuit 3489 is operable to control the duty cycle of the FETQ3482 to adjust the magnitude of the supply voltage V_(CC) to a targetvoltage (e.g., approximately 15 volts).

The junction of the inductor L3484 and the diode D3486 is coupled to theinput capacitor C_(IN) for charging the input capacitor through thesecond output 3474 of the power supply 3470. At the beginning of eachhalf-cycle of the control-hot voltage V_(CH) (i.e., when the magnitudeof the control-hot voltage V_(CH) is approximately zero volts), themicroprocessor 3460 is configured to open the first controllable switch3488, such that the input capacitor C_(IN) is operable to charge fromthe current conducted through the inductor L3484. The microprocessor3460 is configured to also open the second controllable switch 3492 atthe beginning of each half-cycle, such that the magnitude of thefeedback signal V_(PS-FB) is less than the magnitude of the DC supplyvoltage V_(CC). Accordingly, the buck control circuit 3489 tries toincrease the magnitude of the DC supply voltage V_(CC) towards thetarget voltage by increasing the duty cycle of the FET Q3482, such thatthe magnitude of the input voltage V_(IN) across the input capacitorC_(IN) increases. Since the supply capacitor C3480 is disconnected fromthe buck converter, the magnitude of the supply voltage V_(CC) continuesto decrease, and the magnitude of the input voltage V_(IN) continues toincrease. When the magnitude of the input voltage feedback signalV_(IN-FB) indicates that the magnitude of the input voltage V_(IN)across the input capacitor C_(IN) has exceeded an input voltagethreshold V_(IN-TH) (e.g., approximately 100-220 volts), themicroprocessor 3460 closes the first and second controllable switches3488, 3492 to allow the buck converter to once again generate the DCsupply voltage V_(CC) across the supply capacitor C3480. Alternatively,the diode D3494 of the feedback circuit 3490 could comprise two diodescoupled in series or another impedance element for making the magnitudeof the feedback signal V_(PS-FB) to be less than the magnitude of the DCsupply voltage V_(CC) when the buck converter is charging the inputcapacitor C_(IN).

The circuits and methods described herein for charging an inputcapacitor of a power converter circuit (e.g., the input capacitor C_(IN)for the boost converters 1930, 2030, 3230, 3330, 3430) could be used inany electronic ballast, even ballasts that do not communicate using thecommunication techniques described herein (e.g., by transmitting andreceiving forward and reverse digital messages over a circuit wiring).In addition, the circuits and methods described herein for charging aninput capacitor (e.g., the input capacitor C_(IN)) could be used in anytwo-wire load control device (e.g., an LED driver) that may be receivingpower from a phase-control signal (e.g., a forward phase-control signalor a control-hot signal as described herein) to reduce the magnitude ofthe charging current required to charge the input capacitor at thefiring time each half-cycle.

FIG. 45 is a simplified schematic diagram of another example powersupply 3570 for a load control device (e.g., the power supply 3364 ofthe digital dimming ballast 3310 shown in FIG. 43). The power supply3570 receives a bus voltage V_(BUS) that may be generated by a boostconverter (e.g., the boost converter 3430). The power supply 3570comprises a buck converter that is similar in operation as the buckconverter of the power supply 3470 shown in FIG. 44. However, the powersupply 3570 comprises a feedback circuit 3590 that receives the DCsupply voltage V_(CC) across the supply capacitor 3480 and the inputvoltage feedback signal V_(IN-FB), which is representative of themagnitude of the input voltage V_(IN) across the input capacitor C_(IN)of the boost converter 3430. The feedback circuit 3590 comprises a thirdcontrollable switch 3592 and a buffer circuit 3594. The microprocessor3460 generates a feedback circuit control signal V_(FB-CNTL) forcontrolling the third controllable switch 3592 (i.e., to control theswitch between first and second positions).

When the power supply 3570 is charging the supply capacitor C3480, themicroprocessor 3460 closes the first controllable switch 3488 andcontrols the third controllable switch 3592 to a first position, suchthat the supply voltage V_(CC) is coupled to the diode D3495 and themagnitude of the feedback signal V_(PS-FB) is approximately equal to themagnitude of the supply voltage V_(CC). When the magnitude of thecontrol-hot voltage V_(CH) is approximately zero volts, themicroprocessor 3460 opens the first controllable switch 3488, such thatthe input capacitor C_(IN) is operable to charge from the currentconducted through the inductor L3484. At this time, the microprocessor3460 also controls the third controllable switch 3592 to a secondposition to coupled the output of the buffer circuit 3594 to the diodeD3592, such that the magnitude of the feedback signal V_(PS-FB) isrepresentative of the magnitude of the input voltage V_(IN) across theinput capacitor C_(IN). Accordingly, the buck control circuit 3489 willattempt to regulate the magnitude of the input voltage V_(IN) to apredetermined magnitude.

While the present application has been described with reference to thesingle-phase electric power systems shown in FIGS. 1, 20, 22, and 24,the communication techniques of the present invention could also beapplied to two-phase and three-phase electric power systems.

This application is related to commonly-assigned U.S. patent applicationSer. No. 13/359,722, filed Jan. 27, 2012, entitled DIGITAL LOAD CONTROLSYSTEM PROVIDING POWER AND COMMUNICATION VIA EXISTING POWER WIRING, theentire disclosure of which is hereby incorporated by reference.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A load control system comprising: a power device adapted to receivepower from an AC power source via a power wiring; and a controlleradapted to be coupled in series electrical connection on the powerwiring between the AC power source and the power device, the controlleroperable to produce a phase-control voltage that is adapted to bereceived by the power device, the controller operable to transmit aforward digital message to the power device by encoding digitalinformation in timing edges of the phase-control voltage; wherein thepower device is operable to transmit a reverse digital message to thecontroller via the power wiring.
 2. The load control system of claim 1,wherein the controller comprises a controllably conductive deviceadapted to be coupled in series electrical connection between the ACpower source and the power device for generating the phase-controlvoltage.
 3. The load control system of claim 2, wherein a controllervoltage is generated across the controller, the power device operable totransmit a bit of the reverse digital message by adjusting the magnitudeof the controller voltage prior to when the controller renders thecontrollably conductive device conductive during a half-cycle of the ACpower source.
 4. The load control system of claim 3, wherein the reversedigital message comprises a number of sequential data patterns, thecontroller operable to render the controllably conductive deviceconductive to generate a first timing edge at a predetermined referenceedge time during a first half-cycle of each data pattern of the reversedigital message, and to render the controllably conductive device at asecond time during a second half-cycle of each data pattern of thereverse digital message, such that a window time period exists beforethe second time in the second half-cycle, the power device operable toadjust the magnitude of the controller voltage during the window timeperiod to transmit the bit of the reverse digital message.
 5. The loadcontrol system of claim 4, wherein the window time period beginsapproximately a half-cycle time period after the predetermined referenceedge time during the first half-cycle. 6-8. (canceled)
 9. The loadcontrol system of claim 3, wherein the controller comprises a currentpath in parallel with the controllably conductive device and the powerdevice comprises an active load circuit for conducting an active loadcurrent through the current path when the controllably conductive deviceis non-conductive to control the magnitude of the phase-control voltageto approximately zero volts. 10-16. (canceled)
 17. The load controlsystem of claim 3, wherein the power device is operable to transmit thebit of the reverse digital message by adjusting the magnitude of thecontroller voltage to be either greater than or less than a thresholdvoltage during the window time period.
 18. The load control system ofclaim 17, wherein the power device is operable to transmit a logic highbit to the controller by adjusting the magnitude of the controllervoltage to be greater than the threshold voltage during the window timeperiod.
 19. The load control system of claim 17, wherein the powerdevice is operable to transmit an acknowledgement to the controller byadjusting the magnitude of the controller voltage to be less than thethreshold voltage during the window time period. 20-40. (canceled) 41.The load control system of claim 1, wherein the power device is operableto transmit the reverse digital message to the controller in response toreceiving the forward digital message from the controller.
 42. The loadcontrol system of claim 41, wherein the reverse digital message is splitup into a number of packets.
 43. The load control system of claim 42,wherein the controller is operable to transmit a continuation patternbetween the packets.
 44. The load control system of claim 43, whereinthe power device uses a half-cycle period when transmitting the reversedigital message to the controller, the power device operable to updatethe half-cycle time period in response to the continuation pattern. 45.The load control system of claim 43, wherein the controller is operableto transmit a start pattern to begin transmitting a new forward digitalmessage rather than transmitting the continuation pattern after one ofthe packets of the reverse digital message.
 46. The load control systemof claim 42, wherein each packet of the reverse digital message includesan equal number of bits of the reverse digital message. 47-76.(canceled)
 77. The load control system of claim 1, wherein a controllervoltage is generated across the controller, the power device operable totransmit the reverse digital message to the controller by encodingdigital information in the controller voltage. 78-80. (canceled)
 81. Theload control system of claim 1, wherein the load control system isconfigured without accessing the power device or the electrical load.82. (canceled)
 83. The load control system of claim 1, wherein thecontroller comprises a two-wire device.
 84. The load control system ofclaim 1, wherein the controller has a direct connection to the neutralside of the AC power source.
 85. (canceled)
 86. A controller for use ina load control system for controlling the power delivered from an ACpower source to an electrical load, the controller comprising: acontrollably conductive device adapted to be coupled in serieselectrical connection on a power wiring between the AC power source anda power device of the load control system; a control circuit coupled tothe controllably conductive device for rendering the controllablyconductive device conductive each half-cycle of the AC power source togenerate a phase-control voltage, the control circuit is operable totransmit a forward digital message to the power device by encodingdigital information in timing edges of the phase-control voltage; and areverse receiving circuit coupled in parallel electrical connection withthe controllably conductive device; wherein the control circuit isoperatively coupled to the reverse receiving circuit for receiving areverse digital message from the power device via the power wiring. 87.The controller of claim 86, wherein a controller voltage is generatedacross the reverse receiving circuit, the control circuit operable toreceive a bit of the reverse digital message by monitoring the magnitudeof the controller voltage prior to rendering the controllably conductivedevice conductive during a half-cycle of the AC power source.
 88. Thecontroller of claim 87, wherein the reverse digital message comprises anumber of sequential data patterns, the control circuit operable torender the controllably conductive device conductive to generate a firsttiming edge at a predetermined reference edge time during a firsthalf-cycle of each data pattern of the reverse digital message, and torender the controllably conductive device at a second time during asecond half-cycle of each data pattern of the reverse digital message,such that a window time period exists before the second time in thesecond half-cycle, the control circuit operable to monitor the magnitudeof the controller voltage during the window time period to receive thebit of the reverse digital message.
 89. The controller of claim 88,wherein the window time period begins approximately a half-cycle timeperiod after the predetermined reference edge time during the firsthalf-cycle.
 90. The controller of claim 88, wherein the controller isoperable to transmit a continuation pattern before the power device hastransmitted the total number of bits of the reverse digital message. 91.The controller of claim 87, wherein the control circuit operable toreceive the bit of the reverse digital message by determining whetherthe magnitude of the controller voltage is either greater than or lessthan a threshold voltage immediately prior to rendering the controllablyconductive device conductive during the half-cycle of the AC powersource.
 92. The controller of claim 86, further comprising: a currentpath in parallel with the controllably conductive device and operable toconductive current through the power device when the controllablyconductive device is non-conductive, such that the magnitude of thephase-control voltage is approximately zero volts when the controllablyconductive device is non-conductive. 93-111. (canceled)
 112. Thecontroller of claim 86, wherein the forward digital message includes aquery and the reverse digital message includes an answer to the queryfrom the forward digital message. 113-114. (canceled)
 115. Thecontroller of claim 86, wherein the reverse digital message is split upinto a number of packets, the control circuit operable to transmit acontinuation pattern between the packets.
 116. The controller of claim115, wherein the controller is operable to transmit a start pattern tobegin transmitting a new forward digital message rather thantransmitting the continuation pattern after one of the packets of thereverse digital message.
 117. The controller of claim 86, wherein thereverse digital message includes feedback information from the powerdevice.
 118. The controller of claim 117, wherein the control circuit isoperable to transmit the feedback information to an external device.119-124. (canceled)
 125. The controller of claim 86, wherein thecontroller comprises a two-wire device.
 126. The controller of claim 86,further comprising: a neutral terminal adapted to be coupled to theneutral side of the AC power source.
 127. (canceled)
 128. The controllerof claim 86, wherein the control circuit is operable to alternatelyoperate in a dimmer mode and a digital communication mode, the controlcircuit operable to render the controllably conductive device conductiveeach half-cycle at a phase angle that is dependent upon the desiredlighting intensity when operating in the dimmer mode, the controlcircuit operable to transmit a forward digital message by encodingdigital information for controlling the intensity of the lighting loadin the timing edges of the phase-control voltage when operating in thedigital communication mode.
 129. A power device for use in a loadcontrol device for controlling the power delivered from an AC powersource to an electrical load in response to a controller, the powerdevice comprising: a forward receiving circuit adapted to be coupled tothe controller via a power wiring, such that the controller is coupledin series electrical connection between the AC power source and thepower device, the forward receiving circuit operable to receive aphase-control voltage from the controller via a power wiring; a controlcircuit operatively coupled to the forward receiving circuit forreceiving a forward digital message in response to digital informationencoded in timing edges of the phase-control voltage; and a reversetransmitting circuit adapted to be coupled to the controller via thepower wiring; wherein the control circuit is operatively coupled to thereverse transmitting circuit for transmitting a reverse digital messageto the controller via the power wiring.
 130. The power device of claim129, wherein the control circuit is operable to control the reversetransmitting circuit to adjust the magnitude of a controller voltagegenerated across the controller.
 131. The power device of claim 130,wherein the control circuit is operable to transmit a bit of the reversedigital message by adjusting the magnitude of the controller voltageprior to a timing edge of the phase-control voltage during a half-cycleof the AC power source.
 132. The power device of claim 131, wherein thereverse digital message comprises a number of sequential data patterns,each data pattern having a first timing edge at a predeterminedreference edge time during a first half-cycle, the control circuitoperable to adjust the magnitude of the controller voltage during awindow time period during a second half-cycle of each data pattern totransmit the bit. 133-135. (canceled)
 136. The power device of claim131, wherein the control circuit is operable to transmit the bit of thereverse digital message by adjusting the magnitude of the controllervoltage to be either greater than or less than a threshold voltageduring the window time period.
 137. (canceled)
 138. The power device ofclaim 136, wherein the control circuit is operable to transmit anacknowledgement to the controller by adjusting the magnitude of thecontroller voltage to be less than the threshold voltage during thewindow time period.
 139. The power device of claim 131, wherein thereverse transmitting circuit comprises an active load circuit operableto conduct an active load current through the controller before thetiming edges each half-cycle to control the magnitude of thephase-control voltage to approximately zero volts. 140-141. (canceled)142. The power device of claim 129, wherein the control circuit isoperable to transmit the reverse digital message to the controller inresponse to receiving the forward digital message from the controller.143. The power device of claim 142, wherein the reverse digital messageis split up into a number of packets.
 144. The power device of claim143, wherein the control circuit is operable to receive a continuationpattern transmitted by the controller between the packets.
 145. Thepower device of claim 144, wherein the control circuit uses a half-cycleperiod when transmitting the reverse digital message to the controller,the control circuit operable to update the half-cycle time period inresponse to the continuation pattern.
 146. The power device of claim144, wherein the control circuit is operable to received a start patternto begin receiving a new forward digital message rather than receivingthe continuation pattern after one of the packets of the reverse digitalmessage.
 147. The power device of claim 143, wherein each packet of thereverse digital message includes an equal number of bits of the reversedigital message. 148-151. (canceled)
 152. The power device of claim 129,further comprising: a load regulation circuit adapted to be coupled tothe electrical load for controlling the power delivered to the load;wherein the control circuit is coupled to the load regulation circuitfor controlling the power delivered to the load in response to theforward digital message received from the controller. 153-165.(canceled)
 166. The power device of claim 129, further comprising: anoccupancy detection circuit for detecting the occupancy and vacancyconditions in the space around the power device; wherein the reversedigital messages transmitted by the power device comprise informationregarding occupancy and vacancy conditions detected by the occupancydetection circuit.
 167. The power device of claim 129, furthercomprising: a photosensitive circuit for measuring a total light levelaround the power device; wherein the reverse digital messagestransmitted by the power device comprise the total light level measuredby the photosensitive circuit.
 168. The power device of claim 129,wherein the control circuit is operable to detect a number of sequentialdata patterns of the phase-control voltage, each data pattern having afirst timing edge at a reference edge time during a first half-cycle anda second timing edge at a data edge time during a second subsequenthalf-cycle, the control circuit operable to measure an offset timeperiod between the reference edge time and the data edge time of eachdata pattern, and to decode a forward digital message from thecontroller based on the measured offset time periods in each of thesequential data patterns, the control circuit operable to control thepower delivered to the load in response to the forward digital message.169-324. (canceled)